CZ20001937A3 - Prestressed and pre-compressed nozzle of gas turbine - Google Patents

Abstract

The present invention relates to a method of increasing fatigue life low cycle at large turbine nozzle (10) a plurality of stationary profiles (12) arranged between radial inner and outer annular segments (16, 14). The method consists in arranging at least one radial one channel (22) in each of said plurality of profiles (12) installing a rod (56) in said radial channel (22) arranged between the radial inner and outer annular a segment (16, 14) and fastening one end of the rod (56) to one inner and outer ring, and in the prestressing of the rod (56) for compressing the profile between the inner and outer annular segment.

Description

Technical field

The invention relates to ground or industrial gas turbines, for example for generating electric power, and more particularly to a mechanical biasing device for a nozzle wing.

BACKGROUND OF THE INVENTION

Low cycle fatigue (LCF) is one of the main modes limiting the service life of modern industrial gas turbine nozzles. It is caused by cyclic, thermal and mechanical loads occurring during the cycles of gas turbine start-up, operation and shutdown. The effects of these cyclic modes on the low cycle fatigue life generally vary, inter alia, within the "voltage ratio A or the main stress alternation ratio."

For a given cyclic load level, the most harmful low cycle fatigue life cycle is one that includes a period of sustained compression, generally referred to as a stress ratio A or low cycle fatigue stress ratio of -1. Conversely, the least harmful low cycle fatigue life cycle is one that includes a stress-maintaining period of zero, or a stress ratio A stress ratio of low cycle fatigue of +1. Problem • ·

is that the prevailing low cycle fatigue conditions for the nozzle at a reduced life cycle at low cycle fatigue are typically at a voltage ratio A of -1, which results in a low life cycle.

In the past, improving low cycle fatigue life for nozzles has been sought through traditional approaches such as optimizing design to reduce low cycle fatigue stresses and temperatures, as well as choosing new materials with improved low cycle fatigue properties.

In the current gas turbine industry, there is a broad trend of increasing combustion temperatures and developing more efficient nozzle cooling devices, but the stresses and temperatures of the designed nozzles often exceed the capabilities of even the strongest materials currently available.

SUMMARY OF THE INVENTION

The present invention is directed to solving the problem of low cycle fatigue life by biasing the nozzle so that stress ratios A at the life-critical locations are shifted from -1 to +1, resulting in a higher low cycle fatigue life .

In one exemplary embodiment, the OEM mechanical device is intended to bias the nozzle against low cycle fatigue loads, thereby extending its service life beyond normal material limits as compared to the known nozzle. In particular, a biasing rod is inserted into each nozzle or nozzle profile and is fixed at one end, preferably at the radial inner end.

The biasing device, which may be, for example, a threaded nut screwed onto the male threaded surface of the rod, is tightened downwardly on the rod from the outside of the nozzle lid, thereby compressing the profile. After tightening the nut, the rod can be welded to the radial outer lid of the nozzle to achieve the desired preload, thereby fixing the respective preload. The bar is preferably positioned along the leading edge of the profile, since this is the most critical point of the profile in terms of durability. However, if desired, additional rods may be added to other points of the profile.

Therefore, in accordance with the present invention, a method has been developed for increasing the low cycle fatigue life of a turbine nozzle having a plurality of stationary profiles disposed between a radial inner and outer annular segment comprising:

a) arranging at least one radial channel in each of said plurality of profiles,

b) installing a rod in said radial channel disposed between said radial inner and outer annular segments and fastening one end of said rod to one of said inner and outer rings, and

c) biasing said bar to compress said profile between said inner and outer annular segments.

The present invention also relates to a gas turbine nozzle comprising a plurality of profiles disposed between a radial inner and outer annular segment, each profile being provided with means for biasing the profile by compression.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail by way of examples of specific embodiments thereof, the description of which will be given with reference to the accompanying drawings, in which:

Fig. 1 is a partial cross-sectional view of a nozzle vane showing a mechanical biasing device according to a preferred embodiment of the present invention; and Fig. 2 is a cross-sectional view to an enlarged scale of the leading edge cavity of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross-sectional view of a nozzle section, generally designated 10, which constitutes one of a plurality of nozzle sections 10 arranged in a circumferentially positioned system and forming a turbine stage.

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Each nozzle section 10 comprises a vane or profile 12 and respective radially spaced outer and inner walls 14 and 16. These outer and inner walls 14 and 16 are arranged in the form of circumferentially extending hollow annular sections defining, together with the blades 12, an annular hot gas path through the turbine nozzles. degree.

In a preferred embodiment of the nozzle section 10, the radially positioned outer wall or lid 14 is supported by a turbine casing (not shown) carrying structurally the vanes 12 and the radially positioned inner wall 16. The nozzle sections 10 are sealed to one another within the nozzle of a given degree .

The vane or profile 12 comprises a plurality of cavities extending in the radial direction along the length of the vane 12 between the respective outer wall 14 and the inner wall 16, which cavities are spaced one after the other from the leading edge 18 to the rear edge 20. Towards the leading edge 18 to the trailing edge 20, these cavities include a leading edge cavity 22, four successive intermediate cavities 24, 26, 28 and 30, a pair of intermediate cavities 32 and 34, and a trailing edge cavity 36.

The walls defining the cavities shown in cross section lie between the pressure side wall and the suction side wall of the vane 12. This arrangement is evident in Figure 2 with respect to the wall 38.

A pipe or tube 40 is connected to the steam inlet 42 passing through the outer wall 14 for the purpose of supplying cooling steam to the pair of intermediate cavities 32 and 34. The steam outlet 44 is arranged through the outer wall 14 to remove spent cooling steam from the intermediate cavities 24, 26, 28 and 22 Both the leading edge cavity 22 and the trailing edge cavity 36 are respectively provided with separate air inlets 46 and 48.

The insert sleeve 50, provided with a plurality of transverse apertures 52, is disposed within the cavity 22 of the leading edge 18 and is spaced from its inner walls as shown in Figures 1 and 2.

The air flowing through the separate air inlet 46 flows into the insert sleeve 50 and laterally outwardly through the transverse openings 52, so that it strikes the leading edge 22 ' ^{as a} result of which this leading edge 18 is cooled. The cooling air thus used then flows outwardly through openings 54 which are spaced apart from each other along the length of the run-in 22 and are also spaced apart at certain lateral spacings, as shown in FIG. 2.

The intermediate cavities 24, 26, 22 '22' 32 and 34 are provided with similar insert sleeves, which need not be described in further detail for the purposes of the present invention. Further details and details of the refrigerant circuit are described in co-owned pending patent application unknown number (reference number 839-566), filed May 10, 1999. However, it should be noted here that the present invention is equally applicable to other nozzle designs that is, it is not limited to the particular embodiment of the nozzle described herein.

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The biasing rod 56 (preferably of high strength steel) is inserted into the sleeve 50 in the leading edge cavity 22 and extends between the upper surface of the radially positioned outer wall or lid 14 and the lower surface of the lower or radially located inner wall 16. the rod 56 is welded to the lower surface 58 of the inner wall 16, the respective weld being denoted by 60.

The biasing rod 56 extends upwardly through the inner wall 16 and liner sleeve 50 and extends from the radially positioned outer wall or lid 14 by its threaded free end projecting above the upper surface of the lid 14. The biasing device may be in the form of a threaded nut 62 (or may be any other known biasing device), may be tightened relative to the lid 14, thereby applying a compressive biasing load to the blade or profile 12.

Upon completion of this prestressing, the biasing rod 56 may be attached at its upper end by means of a weld designated by reference numeral 64.

Since the leading edge 18 of the blade or profile 12 is the most critical area in terms of durability, it is most effective for the biasing rod 56 to be located in the leading edge cavity 22 or to use a plurality of biasing rods in one or more remaining biases. cavities.

Such preloading of the blades or nozzle profiles will be the stress ratios A in the leading edge regions, of the leading edge regions. · Critical to life, shifted from -1. · · · · · Život uty uty -1 -1 -1 -1 -1 -1 -1 -1 -1 to +1, resulting in a significant improvement in low cycle fatigue life compared to known non-prestressed nozzles. Tests have shown that the low cycle fatigue life can be improved by at least a factor of 2 if the voltage ratio Ά is shifted from -1 to +1.

Although the present invention has been described in connection with its most preferred exemplary embodiment, which is currently considered to be the most practical, it is to be understood that the present invention is not limited to the disclosed embodiment, but is intended to cover a wide range various modifications and equivalent arrangements within the spirit and scope of the following claims.

Claims (2)

PATENT CLAIMS A method of increasing the low cycle fatigue life of a turbine nozzle having a plurality of stationary profiles (12) disposed between a radial inner and outer annular marking segment (16). 14) in that it contains: d) arranging at least one radial channel in each of said plurality of profiles (12), e) installing a rod (56) in said radial channel disposed between said radial inner and outer annular segments and fastening one end of said rod to one of said inner and outer rings, and f) biasing said bar (56) to compress said profile between said inner and outer annular segments. The method of claim 1, wherein during step b), the lower end of said rod (56) is attached to said inner annular segment (16) and the free end of said rod (56) extends radially through said profile and said outer annular segment (14), wherein the nut (62) is threadedly connected to said rod (56) and is tightened against said outer annular segment so as to bias said profile (12) by compression. Φ Φ Φ «Φ Φ Φ Φ φ φ · · · φ 4 4 φ φ 4 4 4 4 Φ Φ Φ Φ φ φ φφ ΦΦΦ • Φ φφ 3. Method according to claim 2, mark í c and by that after tightening the nut (62) is rod (56) welded to the outer annular segment (14). 4. Method according to claim 3, mark í c and by that steps a) b) a c) are repeated for each nozzle profile. 5. Method according to claim 1, mark í c and by that sleeve (5Ό) is positioned in said at least one radial channel (22), said rod (56) extending through said sleeve (50). 6. Method according to se t Italy (22) claim 1, at least náběhové characterized one radial nozzle edges (18) c í channel (10). í m Yippee that said placed along 7. Method according to claim 6, characterized c í se t í m that said radial the channel (22) comprises a cooling channel. 8. Nozzle for gas turbine, characterized c í se t í m that it contains big a plurality of profiles (12) disposed between the radial inner and outer annular segments (16, 14), each profile (12) being provided with means (56, 62) for biasing said profile (12) by compression. 9. A nozzle as claimed in claim 1, wherein each of the nozzles is of the following type: 8 99 99 9 9 9 9 9 9 · 9 • 4 9 · 9 9 • 9 9 9 »· 9999 9 9 9 9 9 · 9 9 9 9 9 9 · 9 99 9 9 9 at least one radial channel (22) extending between said inner and outer annular, said profile biasing means comprising a rod extending through said channel. the profile has essentially a segment, said radial A nozzle according to claim 9, characterized in that said radial channel extends along the leading edge of said profile. The nozzle of claim 9, wherein said rod is attached to said radial inner annular segment, wherein said biasing is applied to said radial outer annular segment. 12. A gas turbine nozzle comprising a plurality of profiles extending between a radial inner and an outer annular segment, each profile having a biasing rod extending radially therethrough, said biasing rod having one end attached to one of said blades. radially inner and outer annular segments, and the opposed threaded free end is provided with a threaded nut, said profile being compressed by tightening said threaded nut against said radial outer annular segment. Nozzle according to claim 12, characterized in that said biasing rod extends radially along the leading edge of said profile.