Singlet welded nozzle hybrid design for a turbine
A singlet welded nozzle hybrid design that includes a singlet, that is, a single airfoil with respective inner and outer sidewall components. The outer sidewall component is received in a radial and circumferential groove of an outer carrier. The connection of the inner sidewall can be achieved by mechanically fitting and welded the inner sidewalls to either a seal carrier or a small ring, or a small radial weld may be provided between the sidewall endfaces of circumferentially adjacent singlets.
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Steam turbine designs consist of static nozzle segments that direct the steam flow into rotating buckets that are connected to a rotor. In steam turbines, the nozzle construction is typically called a diaphragm stage. Typical diaphragm stages are constructed using one of two methods. The first method is a “band/ring” method that uses an assembly comprised of a plurality of airfoils contained in inner and outer bands and then that banded airfoil assembly is welded into inner (web) and outer rings. The second method involves welding airfoils directly to inner and outer rings using a fillet weld at the interface. The second method is typically used for larger airfoils, where access for creating the weld is possible. However, there are also limitations to using the band construction on smaller stages. One drawback is the inherent weld distortion of both the flow path and the steam path sidewalls. In this regard, the weld used for the assembly is of considerable size and heat input. This material and heat input causes the flow path to distort and the airfoils often need to be adjusted after welding and stress relief. The result of the distortion is reduced stage efficiency.
In turbines, thermally induced stresses have always led to cracking in turbine nozzles. Due to the harsh environment, previous field history has shown cracking along the engine axial (chordwise) direction of nozzle airfoils. Should a crack propagate through the entire length of an airfoil, such that the airfoil fails catastrophically, large pieces of the nozzle might dislodge and move downstream into a turbine's rotating hardware. The subsequent damage to the turbine's hardware (both rotating and static) can be both extreme and costly.
In doublet or triplet nozzle designs (2 or 3 airfoils per nozzle segment, respectively), the increased number of airfoils provides a certain amount of insurance against catastrophic failure through the redundancy of multiple load paths. However, with a singlet design (one airfoil per nozzle segment), if not retained at both platforms, a large section of nozzle (airfoil and/or platform) could be lost into the flowpath if the airfoil were to crack completely in two.
BRIEF DESCRIPTION OF THE INVENTIONThe invention provides a singlet welded nozzle hybrid design which inter alia addresses the distortion problem noted above. More particularly, in an example embodiment of the invention a construction is provided wherein a singlet (single airfoil with sidewalls) is seated directly in a radial and circumferential groove of an outer carrier or welded to an outer ring and seated with in a groove of an outer carrier. The inner connection is effected with a unique inner sidewall construction. In one example embodiment, the inner sidewalls are mechanically fit and welded to a circumferentially extending ring, or to one another via a small radial weld between inner sidewall endfaces (slashfaces).
Thus, the invention may be embodied in a turbine comprising: a turbine nozzle segment having at least one stator airfoil, an inner sidewall at a radially inner end of the stator airfoil, and an outer sidewall structure at the radially outer end of said stator airfoil, a radially inner surface of the inner sidewall having a circumferential groove defined therein, and a complimentary ring component having a key portion for being received in said circumferential groove, said ring component extending at least part circumferentially of an axis of the turbine to engage an inner sidewall of at least two respectively adjacent nozzle inner sidewalls, wherein the ring component is mechanically secured to the nozzle inner sidewalls.
The invention may also be embodied in a turbine comprising: a turbine nozzle segment having at least one stator airfoil and including an inner sidewall at a radially inner end of the stator airfoil and an outer sidewall structure at the radially outer end of said stator airfoil; and an outer ring carrier having a radially inwardly open groove; wherein said outer sidewall is configured to slideably engage said groove in a radial direction while being restricted from moving in an axial direction with respect thereto, and the inner sidewall is mechanically coupled to circumferentally adjacent turbine nozzle segments.
The invention may also be embodied in a turbine comprising: a turbine nozzle segment having at least one stator airfoil and including an inner sidewall at a radially inner end of the stator airfoil and an outer sidewall structure at the radially outer end of said stator airfoil, wherein respectively adjacent nozzle inner sidewall endfaces are welded or braised together.
As noted above, current methods of construction incorporating single nozzle constructions into rings do not have determinant weld depth, lack assembly alignment features, and also lack retainment features in the event of weld failure. Additionally, one major issue with current methods of diaphragm construction is that they can cause significant flow path distortion. Indeed, traditional singlet nozzle assemblies may use high heat input weld methods that cause undesired flow path distortion.
The present invention improves the steam path flow path of the stator nozzle (diaphragm) components. This is done with a simplified, determinant, low heat input singlet welded assembly using novel approaches at the inner sidewall connection such as, for example, welded endwalls, low heat input seal welds with mechanical lock, or small ring key welded to inner sidewalls, as described hereinbelow. The invention also improves the production cost and cycle by adding features that assist in assembly procedures and that assist in machining fixturing. Further, the invention adds features that reduce the risk of unintended turbine shut down due to hardware weld failure.
The singlet welded nozzle hybrid design provided according to example embodiments of the invention creates a construction that includes a singlet, that is, a single airfoil with respective inner and outer sidewall components. The outer sidewall component mechanically fit and then welded to an outer ring carrier.
The connection of the inner sidewall can be achieved in several ways. As described in various embodiments hereinbelow, the inner sidewalls of the singlets of the diaphragm can be mechanically fit and welded to either a seal carrier or a small ring, or a small radial weld may be provided between the sidewall endfaces (slashfaces) of circumferentially adjacent singlets. This construction is suited primarily to nozzle constructions that are considered reaction-type turbines or “drum” construction turbine sections, characterized by much smaller axial spacing of the stages and a typically increased number of stages.
According to example embodiments, the radially inner sidewalls 32 of circumferentially adjacent singlets are coupled. According to certain example embodiments, an inner ring 52 may be keyed and welded 54, 56 to the construction. The keyed inner ring may define a seal carrier. According to another, alternative example embodiment, the singlet inner sidewalls 32 are welded to each other at their abutting endfaces. Examples the above mentioned assemblies are described in greater detail below with reference to
In this example embodiment, the inner ring 152 is configured to also comprise a seal carrier. The seal carrier is very small in design such that it can fit in the small axial and radial spacing typical of drum construction turbine types. This is generally different from the significant real estate required to hold the traditional packing segments at the rotor interface. Thus, the proposed carrier would facilitate the more advanced seals, i.e., brush seals, shingle type seals or abradable seals. This carrier could also be coated with abradable spray prior to assembly and the small seal welds could be machined away for ring removal when a repair (re-coat) is required. In the example embodiment of
As mentioned above with reference to
The mechanical features of the interface between the singlet and the outer ring 538 are used as an assembly and alignment feature and allow for improved reliability and risk abatement. In this regard, the mechanical lock between the ring and nozzle(s) means that, in the even of failure of an airfoil, the rings and nozzles cannot go downstream as there is a mechanical interference preventing the assembly from failing due to the pressure. Additionally, the mechanical lock serves the purpose of a pre-determined and repeatable weld stop. In this regard, the weld beam (assuming an EB weld) would stop when it hits the radial interlock interface. A further advantage of the
The example embodiment of
While as mentioned above the typical singlet nozzle outer wall interface is a circumferentially cut end, it is to be understood that as an alternative the singlet nozzle outer sidewall interface may be machined as a flat end which is less costly than a circumferential cut end.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims
1. A turbine comprising:
- a turbine nozzle segment having at least one stator airfoil, an inner sidewall at a radially inner end of the stator airfoil, and an outer sidewall structure at the radially outer end of said stator airfoil, a radially inner surface of the inner sidewall having a circumferential groove defined therein, and a complimentary ring component having a key portion for being received in said circumferential groove, said ring component extending at least part circumferentially of an axis of the turbine to engage an inner sidewall of at least two respectively adjacent nozzle inner sidewalls, wherein the ring component is mechanically secured to the nozzle inner sidewalls.
2. A turbine as in claim 1, wherein the ring component is welded to the nozzle inner sidewalls.
3. A turbine as in claim 1, wherein said ring component comprises a seal carrier.
4. A turbine as in claim 3, wherein said seal carrier is a brush-type seal carrier.
5. A turbine as in claim 3, wherein said seal carrier is a laminated-type seal carrier.
6. A turbine as in claim 3, wherein said seal carrier is welded to said nozzle inner sidewall.
7. A turbine as in claim 3, wherein a radial bolt is disposed to extend through said seal carrier and into said nozzle inner sidewall.
8. A turbine as in claim 1, wherein a radial bolt is disposed to extend through said ring component and into said nozzle inner sidewall.
9. A turbine as in claim 1, wherein said outer sidewall is slidably disposed in a nozzle carrier of the turbine.
10. A turbine as in claim 9, wherein the outer sidewall is welded to a solid ring disposed radially outwardly of said turbine nozzle and extending circumferentially about a plurality of said nozzle segments.
11. A turbine comprising:
- a turbine nozzle segment having at least one stator airfoil and including an inner sidewall at a radially inner end of the stator airfoil and an outer sidewall structure at the radially outer end of said stator airfoil; and
- an outer ring carrier having a radially inwardly open groove; wherein
- said outer sidewall is configured to slideably engage said groove in a radial direction while being restricted from moving in an axial direction with respect thereto, and
- the inner sidewall is mechanically coupled to circumferentally adjacent turbine nozzle segments.
12. A turbine as in claim 11, wherein said outer sidewall is welded to an outer ring that is slideably received in said groove with said outer sidewall.
13. A turbine as in claim 12, wherein said outer sidewall has a flat radially outer face that engages a flat radially inner face of said outer ring.
14. A turbine as in claim 12, wherein outer ring extends part circumferentially and is welded to a plurality of said outer sidewalls.
15. A turbine as in claim 11, respectively adjacent nozzle inner sidewall endfaces of said circumferentally adjacent turbine nozzle segments are welded or braised together.
16. A turbine as in claim 11, wherein said inner sidewall has a circumferential groove defined therein and a complimentary ring component having a key portion for being received in said circumferential groove, said ring component extending at least part circumferentially of an axis of the turbine to engage an inner sidewall of at least two respectively adjacent turbine nozzle segments, and wherein the ring component is mechanically secured to the nozzle inner sidewalls.
17. A turbine as in claim 16, wherein the ring component is welded to the nozzle inner sidewalls.
18. A turbine comprising:
- a turbine nozzle segment having at least one stator airfoil and including an inner sidewall at a radially inner end of the stator airfoil and an outer sidewall structure at the radially outer end of said stator airfoil, wherein respectively adjacent nozzle inner sidewall endfaces are welded or braised together.
19. A turbine as in claim 18, wherein said outer sidewall is slidably disposed in a circumferential groove defined in a nozzle carrier of the turbine.
20. A turbine as in claim 19, wherein said outer sidewall is welded to an outer ring that is slideably received in said circumberential groove with said outer sidewall.
Type: Application
Filed: Aug 23, 2006
Publication Date: Feb 28, 2008
Applicant: GENERAL ELECTRIC COMPANY (Schenectady, NY)
Inventors: Steven Sebastian Burdgick (Schenectady, NY), Thomas William Crall (Clifton Park, NY), Larry Duclos (Thorndike, ME), Thomas Patrick Russo (Galway, NY)
Application Number: 11/508,170
International Classification: F04D 29/08 (20060101);