Nozzle arc segment, steam turbine with multiple nozzle arc segment diaphragms, and diaphragm assembly method

Abstract

The present invention relates to an integrated or monolithic nozzle segment (30) having an airfoil (33). According to one aspect of the invention, a steam turbine has a casing (17) supporting a plurality of nozzle segments (30) forming a diaphragm (22) with an airfoil (33) located in a passage (23) through which working fluid flows. The diaphragm (22) coaxially surrounds an axis of rotation (A) of the steam turbine (15) and is comprised of a plurality of individual nozzle segments (30). The nozzle segments (30) and the casing (17) of the steam turbine (15) have substantially equal coefficients of thermal expansion. The casing (17) and the nozzle segments (30) are made of different materials and, in particular, different types of martensitic steel. According to another aspect of the invention, each nozzle segment (30) has a core (37) comprising a martensitic steel having a minimum creep strength at a temperature of 580°C satisfying the following condition: at least 10 5 hours under a tensile stress of at least 100 MPa or at least 125 MPa or at least 150 MPa.

Description

[0001] The present invention relates to a nozzle arc segment of a diaphragm, a steam turbine having a housing and a diaphragm attached to the housing, and a method for assembling the diaphragm.

[0002] US 2006 / 0245923 A1 discloses an arrangement of turbine nozzle segments including a first ring segment, a second ring segment, and a plurality of airfoil elements extending between the first ring segment and the second ring segment. The nozzle segments are made of solid rings.

[0003] A nozzle box made of individual nozzle segments is known from US7207773B2, each nozzle segment comprising multiple airfoil elements. The working fluid flows through the nozzle box in an axial direction parallel to the turbine's axis of rotation.

[0004] US4,776,765A relates to a technique for reducing solid particle corrosion by providing a protective device over at least a portion of the suction side of a nozzle section. The nozzle may be made of martensitic chromium stainless steel and have a surface coating as a protective device.

[0005] Further embodiments of the commonly known nozzle arrangement are described in US4,025,229A, US5,807,074A, US6,631,858B1, US6,754,956B1 and US2003 / 0103845A1.

[0006] US4,948,333A discloses a baffle supported by a turbine casing for redirecting radial working fluid flow. The baffle includes two rings extending coaxially with the turbine's axis of rotation and supporting an airfoil between the two rings. The airfoil deflects a substantially radially oriented working fluid flow upstream of the baffle into a direction that includes a component of the working fluid flow in the circumferential direction about the axis of rotation. A similar baffle is also disclosed in EP3412872B1.

[0007] Another device for deflecting working fluid flow from the radial direction to the axial direction is known from US7,670,109B2.

[0008] Some types of steam turbines include diaphragms for directing the flow of working fluid into the first stage of a turbine rotor blade connected to a rotatable rotor. The rotor includes a shaft that extends in the axial direction and defines an axis of rotation. The diaphragm may also be referred to as a "nozzle assembly." The diaphragm includes multiple airfoil elements that may be referred to as "nozzles."

[0009] In the past, at least some steam turbines have suffered damage to their diaphragms, such as partial cracking, bending, or even breakage of airfoil components. To mitigate these failures and increase component reliability and lifespan, measures have been taken to reduce thermal stress on components, for example, by increasing the radial and axial clearances in the connection between the diaphragm and the turbine casing. However, depending on the operating conditions, increased clearances can lead to efficiency losses due to leakage of the working fluid.

[0010] Therefore, it is desirable to provide a steam turbine with diaphragms that offer high reliability and long service life while allowing for simplified assembly. Specifically, the steam turbine will be configured for operating temperatures above 570°C for the working fluid (the ultra-supercritical temperature range of the working fluid).

[0011] This objective is achieved by the nozzle arc segment according to claim 1, the steam turbine according to claim 11, and the method of assembling the diaphragm to the housing according to claim 16.

[0012] The steam turbine includes a casing surrounding at least one turbine pressure section having multiple rows of fixed guide vanes coupled to the casing and rotatable rotor blades coupled to the rotor of the steam turbine.

[0013] To direct the working fluid in at least one turbine pressure section, a diaphragm is attached to the casing, particularly downstream of the inlet passage and upstream of the first turbine pressure section. The diaphragm is specifically configured to direct the flow of working fluid toward the rotor blades. In one embodiment, the diaphragm is annular and coaxially positioned around the axis of rotation of the turbine rotor.

[0014] The diaphragms of a steam turbine may include separate diaphragm segments, each of which may extend substantially in a semi-circular manner about the turbine's axis of rotation. Each diaphragm segment is attached to a portion of the turbine casing (e.g., a portion of the casing).

[0015] In one aspect of the invention, a nozzle segment is provided for a diaphragm of a steam turbine. Each nozzle segment includes a first ring segment and a second ring segment, which extend parallel to each other and are spaced apart from each other in the axial direction. The first and second ring segments support a plurality of airfoils extending from the first ring segment to the second ring segment and defining a nozzle opening between two directly adjacent airfoils. The first ring segment may be referred to as a root, and the second ring segment may be referred to as a shroud. Preferably, when viewed or measured in the axial direction, the thickness of the shroud is less than the thickness of the root. For example, each nozzle segment may include 8 to 12 airfoils. The diaphragm may include 8 or more nozzle segments. However, the number of nozzle segments may vary in different embodiments.

[0016] The first and second ring segments of each nozzle arc extend along an arc around the turbine's axis of rotation. All nozzle arc segments together form a circular annular baffle.

[0017] According to one aspect of the invention, the coefficient of thermal expansion of each nozzle arc segment is substantially equal to the coefficient of thermal expansion of the supporting nozzle arc segment of the turbine casing. Preferably, the coefficient of thermal expansion of each nozzle arc segment differs from that of the casing by at most 5%, 3%, or 2% over a temperature range up to 600°C.

[0018] According to a preferred embodiment of the invention, each nozzle segment has a core comprising martensitic steel having a minimum creep rupture strength at a temperature of 580°C that satisfies the following condition: at least 10 MPa under a tensile stress of at least 100 MPa, at least 125 MPa, or at least 150 MPa. 5 No fracture within hours. Creep fracture strength is determined by measuring the duration of time it takes for the material probe to fracture under a defined tensile stress. This characteristic can also be used independently of the difference in thermal expansion coefficients between the housing and the nozzle arc segment.

[0019] Specifically, the martensitic steel for the core can be X17CrMoVNbB9-1, commonly referred to as "Steel B," or alternatively, X22CrMoV12-1, type 1.4923. Other steels can also be used to manufacture nozzle arc 30, such as X10CrWMoVNb9-2, X14CrMoVNbN10-2, 9Cr-3W-3Co-VNbBN, or X13CrMoCoVNbNB9-2-1, provided that their coefficients of thermal expansion are substantially equal to those of the shell.

[0020] In a preferred embodiment, the airfoil, first ring segment, and second ring segment of each nozzle arc segment are integrally or monolithically made of the same material without seams or joints. For example, each nozzle arc segment can be machined from a single solid initial workpiece. During machining, material can be removed from the solid workpiece (e.g., by milling or etching) to obtain the desired configuration of the nozzle arc segment. Alternatively, each nozzle arc segment can be manufactured using additive manufacturing techniques. In this embodiment, specifically, each nozzle arc segment has no welded joints, adhesive joints, profile mating joints, or material bonding between the airfoil and the ring segment.

[0021] Alternatively, in another embodiment, the airfoil and the ring segment can be manufactured separately and then joined together to form the nozzle arc segment. Specifically, the connection between the airfoil and the ring segment can be established by welding a joint.

[0022] It is advantageous if the core of each nozzle segment is coated with a surface coating in at least one or more surface areas. Due to the surface coating, the nozzle segments can be made less sensitive to high-temperature oxidation and solid particle corrosion compared to the material of the nozzle core.

[0023] The surface coating may contain at least one of the following: chromium, carbon, and nickel. In one embodiment, the surface coating may contain chromium carbide (Cr3C2), nickel-chromium (NiCr), or a combination thereof.

[0024] The surface area with the surface coating is preferably located on the surface of the airfoil. The surface coating may partially or completely cover the surface of the airfoil. Alternatively, the surface coating may additionally cover at least a portion of the first or second ring segment of the nozzle arc, preferably covering the surface area subjected to the working fluid flow.

[0025] The surface coating can be applied to at least one surface area of ​​the nozzle arc segment by thermal spraying, preferably high-velocity oxygen fuel spraying (HVOF) or high-velocity air fuel spraying (HVAF). For example, the coating material in powder form can be supplied to the burner and ejected by a high-velocity gas jet onto at least one surface area to be coated. The surface area to be coated can be roughened before the coating material is applied to improve adhesion.

[0026] By providing a nozzle arc segment that includes multiple airfoils, larger units can be handled during the assembly and disassembly of the baffle. Compared to baffle configurations with individual airfoils, the nozzle arc segment is less susceptible to irritation caused by the working fluid flow.

[0027] The material of the housing supporting the nozzle arc segment is different from the material of the nozzle arc segment. Specifically, the material of the nozzle arc segment has a higher creep strength than the material of the housing supporting the nozzle arc segment.

[0028] The nozzle arc undergoes length changes due to temperature variations. This can lead to mechanical stresses that may reduce diaphragm life or cause malfunctions during operation. Because the coefficients of thermal expansion of the nozzle arc and the casing are substantially equal over the relevant temperature range—specifically, from 570°C to 650°C—the nozzle arc is allowed to expand or contract similarly to the casing. This reduces mechanical stress on the components. Clearances between directly adjacent nozzle arcs and between the nozzle arc and the supporting structure of the casing can be minimized during installation. Therefore, not only is the reliability of the turbine improved, but its efficiency is also enhanced.

[0029] As the material for the housing used to support the nozzle arc segment, a different martensitic steel than the martensitic steel used in the core of the nozzle arc segment can be used. For example, the martensitic steel used for the housing can be of type GX12CrMoVNbN9-1 1.4955 as defined in EN10213 "Steel castings for pressure purposes".

[0030] In a preferred embodiment of the steam turbine, each nozzle segment corresponds to an embodiment of a nozzle segment according to a first aspect of the invention.

[0031] A preferred embodiment of the steam turbine includes two opposing casing recesses, both open on their respective facing sides. These casing recesses form a support structure for the casing, configured to support nozzle arc segments. The casing recesses may extend coaxially or circumferentially around the turbine's axis of rotation. Each nozzle arc segment engages a first casing recess with a first annular segment and a second casing recess with a second annular segment. The casing recesses are arranged spaced apart from each other in the axial direction. In this configuration, the airfoils of the nozzle arc segments are arranged in the gaps between the casing recesses in the flow path of the working fluid.

[0032] The turbine casing may include a first casing half and a second casing half. A set of nozzle segments may be arranged in the first casing half forming a first diaphragm section. Another set of nozzle segments may be arranged in the second casing half forming a second diaphragm section. The two separate diaphragm sections allow for easy assembly and disassembly of the turbine casing halves.

[0033] Preferably, at least the outermost nozzle arc segment of each partition segment is secured in each case by at least one fixing element to prevent movement along the extension direction of the housing groove. The fixing element can, in each case, establish a profile fit and / or press-fit connection between the outermost nozzle arc segment and the housing half. The outermost nozzle arc segments are those nozzle arc segments in each housing half that directly abut the separation plane along which the first and second housing halves are connected. By securing the outermost nozzle arc segments, the intermediate nozzle arc segments of each partition segment are also maintained between the two outermost nozzle arc segments of each partition segment.

[0034] In one embodiment of the turbine, each nozzle segment may have an annular groove in one of the annular segments, preferably in the first annular segment. The turbine casing, specifically both casing halves, has arcuate protrusions that engage with the annular grooves of the corresponding nozzle segments. Thus, an arcuate protrusion of the first casing half engages with the annular groove of the nozzle segment forming the first diaphragm segment, and an arcuate protrusion of the second casing half engages with the annular groove of the nozzle segment forming the second diaphragm segment. Preferably, each arcuate protrusion extends radially from the sidewall of one of the casing grooves relative to the turbine's axis of rotation.

[0035] The diaphragm or diaphragm section can be assembled with the turbine casing or casing half in the following manner:

[0036] For the components, nozzle segments are provided, each nozzle segment including a first annular segment, a second annular segment, and a plurality of airfoil elements extending from the first annular segment to the second annular segment. A turbine casing is provided having a first casing half and a second casing half. The first casing half may be an upper casing half, and the second casing half may be a lower casing half, or vice versa. Each casing half is provided with semicircular first casing recesses and semicircular second casing recesses arranged opposite to each other.

[0037] The provided nozzle arc segment grooves are used to form a first partition segment in the first housing half. For this purpose, one nozzle arc segment is inserted into the opposing housing groove and moved to the desired position. The nozzle arc segment is clamped in this desired position by any suitable clamping device, such as a clamp or brake bar inserted between the nozzle arc segment and the wall of the first or second housing groove. Subsequently, the other nozzle arc segments of the first partition segment are inserted into the housing grooves of the first housing half in a similar manner. Where necessary or advantageous, spacers may be arranged between directly adjacent nozzle arc segments of the first partition segment.

[0038] The second partition section is similar to the first partition section and is assembled in the second housing half.

[0039] Preferably, the outermost nozzle segment of each partition section is secured to the corresponding housing half by at least one fixing element, such as a fixing pin. The outermost nozzle segments of each partition section are two nozzle segments directly adjacent to the separation plane between the first and second housing halves. The housing halves are attached to each other along the separation plane. Preferably, the separation plane extends in a horizontal direction.

[0040] If the outermost nozzle arc segment of each partition section is fixed by a fixing device, specifically a fixing pin, then the gap shim can be removed subsequently, so that the nozzle arc segments of each partition section are arranged adjacent to each other with a defined gap.

[0041] Where necessary, the fixing element, specifically the fixing pin, can be processed or machined to have a desired external profile that aligns with the external profile of the adjacent nozzle arc segment, such that when the first and second housing halves are attached to each other, there is no interference or obstruction to the connection of the two baffle segments. When the housing halves are attached to each other, the baffle segments form a closed loop, which is preferably arranged coaxially about the turbine's axis of rotation.

[0042] Preferred embodiments of the steam turbine and method are disclosed in the dependent claims, specification, and drawings. The preferred embodiments of the invention will be explained in detail below with reference to the accompanying drawings, in which:

[0043] Figure 1 A cross-sectional view is shown along the axis of rotation of an embodiment of a steam turbine having a casing and diaphragms attached to the casing within the flow path of the working fluid.

[0044] Figure 2 yes Figure 1 The enlarged view of part II, showing the arrangement of the partitions on the housing, is shown in the figure.

[0045] Figure 3 This is a perspective view of an implementation scheme for a partition formed by multiple arc-shaped nozzle segments;

[0046] Figure 4 yes Figure 3 A perspective view of one embodiment of the nozzle arc segment;

[0047] Figure 5 It is a schematic diagram of a first housing half having a first partition section and a second housing half having a second partition section;

[0048] Figures 6 to 8 The assembly steps are shown during the fitting of the nozzle arc segment into the casing groove of the turbine casing;

[0049] Figure 9 This is a flowchart of an embodiment of an assembly method for mounting a diaphragm onto the casing of a steam turbine;

[0050] Figure 10 The coefficients of thermal expansion of different steels depending on temperature are shown; and

[0051] Figure 11 and Figure 12 A schematic cross-sectional view of an airfoil passing through the nozzle arc is shown.

[0052] Figure 1An embodiment of the steam turbine 15 is shown in cross-sectional view along the axis of rotation A. The axis of rotation A is defined by a shaft 16 rotatably supported on a casing 17 of the steam turbine 15. According to a preferred embodiment, the casing 17 includes a first casing half 17a and a second casing half 17b attached to each other along a preferably horizontally extending separation plane P. Figure 3 and Figure 5 The separation plane P is schematically shown in the diagram.

[0053] The steam turbine includes at least one pressure section and may have multiple pressure sections such as a high-pressure section and a medium-pressure section. Each pressure section includes fixed guide vanes 18 arranged in a ring around the axis of rotation A and connected to the casing 17. The rotating blades 19 and the shaft 16 of each pressure section are part of the turbine rotor 20.

[0054] To drive the rotor 20, a working fluid flows along a fluid path inside the housing 17, in which fixed guide vanes 18 and rotating blades 19 are arranged. The working fluid is used to rotate the rotor 20 about the axis of rotation A.

[0055] In this specification, the axial direction D is the direction parallel to the axis of rotation A. Any direction radial to the axis of rotation A is called the radial direction. The direction along a circular path around the axis of rotation A or the axial direction D is called the circumferential direction C.

[0056] Upstream of the first pressure section, the turbine includes an inlet passage 21, which may also be referred to as an inlet vortex tube. The inlet passage 21 extends within the casing 17 in a circumferential direction C about the axis of rotation A. A baffle 22 is arranged to guide the working fluid flow from downstream of the inlet passage 21 and upstream of at least one pressure section through a fluid connection passage 23. The inlet passage 21, baffle 22, and fluid connection passage 23 correspond to... Figure 1 Section II marked in the middle Figure 2 The enlarged view shows a portion of the flow. The working fluid flow upstream of baffle 22 is substantially radially toward the axis of rotation A. Baffle 22 is configured to deflect this flow such that it includes a flow direction component in the circumferential direction C.

[0057] A fluid connection channel 23 fluidly connects the inlet channel 21 to at least one pressure section of the turbine 15. Adjacent to the fluid connection channel 23, the housing 17 includes a first housing recess 24 and a second housing recess 25 arranged to be spaced apart from each other in the axial direction D. The housing recesses 24 and 25 are aligned such that their open sides face each other in the axial direction D. The fluid connection channel 23 extends between the housing recesses 24 and 25. The housing recesses 24 and 25 extend coaxially with the axis of rotation A. They are configured to support a partition 22 such that the partition 22 extends coaxially about the axis of rotation A of the turbine 15.

[0058] refer to Figure 3 and Figure 4 The partition 22 includes multiple nozzle segments 30. Each nozzle segment 30 extends in an arc shape in the circumferential direction C about the axis of rotation A. All nozzle segments 30 together form a closed loop.

[0059] According to a preferred embodiment, the baffle 22 includes eight nozzle arc segments 30. It should be noted that the number of nozzle arc segments 30 of the baffle 22 can vary, and in other embodiments can be smaller or larger.

[0060] like Figure 4 As clearly shown, each nozzle segment 30 includes a first annular segment 31 and a second annular segment 32. These two annular segments are arranged spaced apart from each other in the axial direction. A plurality of airfoils 33 extend between the first annular segment 31 and the second annular segment 32, such that the annular segments 31, 32 are connected to each other by the plurality of airfoils 33, and thus form an integral or monolithic nozzle segment 30. The number of airfoils 33 in each nozzle segment 30 can vary, and according to this example, each nozzle segment may contain 8 to 12 airfoils 33.

[0061] Two directly adjacent airfoil elements 33 of the nozzle arc 30 restrict the flow of working fluid through an opening 34 of the baffle 22. (Example) Figure 2 As best shown, airfoil 33 and opening 34 are arranged in fluid connection channel 23 such that working fluid can flow from inlet channel 21 toward at least one pressure section of turbine 15 via opening 34 of diaphragm 22.

[0062] from Figure 3 and Figure 4It is evident that adjacent nozzle arc segments 30 have a first end face 35 at the circumferential end of a matching first ring segment 31 and a second end face 36 at the circumferential end of a second ring segment 32. The end faces 35, 36 at each circumferential end of the nozzle arc segment 30 preferably extend in a common intermediate plane S. This intermediate plane S can be aligned in one dimension parallel to the axial direction D and can be inclined relative to the circumferential direction C. This means that the intermediate plane S is not oriented orthogonal to the circumferential direction C, but rather includes an acute angle α relative to the circumferential direction C, such as... Figure 4 and Figure 7 As schematically shown. Angle α can be equal for all intermediate planes S between two directly adjacent nozzle arc segments 30.

[0063] Due to the inclined end faces 35 and 36, an overlapping region is obtained, in which the corresponding first ring segment 31 and second ring segment 32 overlap. The overlapping regions are respectively located inside the first housing groove 24 and the second housing groove 25.

[0064] exist Figure 5 The housing 17, comprising a first housing half 17a and a second housing half 17b, is shown schematically at medium height. Semicircular sections of housing recesses 24 and 25 are disposed in the first housing half 17a, and other semicircular sections of housing recesses 24 and 25 are disposed in the second housing half 17b. A set of nozzle arc segments 30 arranged in the first housing half 17a forms a first partition segment 22a, and nozzle arc segments 30 arranged in the second housing half 17b form a second partition segment 22b. Each partition segment 22a, 22b extends substantially semicircularly. In the fully assembled state, the two partition segments 22a, 22b form an annular partition 22 coaxially arranged around the axis of rotation A. In this assembled state, the two housing halves 17a, 17b are connected to each other along the separation plane P.

[0065] The shell 17 and the shell halves 17a and 17b according to this example are made of a steel alloy containing martensitic steel. Preferably, at least the support structure of the shell halves 17a and 17b, including the shell recesses 24 and 25, contains martensitic steel or is made of martensitic steel. The martensitic steel used for the shell 17 is preferably a steel of the Stg9T type. The temperature-dependent normalized coefficient of thermal expansion of the steel type Stg9T is... Figure 10 As shown in the image.

[0066] Considering the different requirements regarding the mechanical properties of the shell 17 and the diaphragm 22, the steel type used for the shell 17 is unsuitable for manufacturing the diaphragm 22. In previous steam turbines, the diaphragm 22 was made of steel type X10CrNiW17-13-3, particularly for applications where the working fluid temperature is greater than 570°C (ultra-supercritical conditions). However, additional measures must be taken to bond this austenitic material to the shell, for example by inserting an intermediate layer, such as an alloy 617 weld layer, into the second shell recess 25, to accommodate the different mechanical properties of the steel types used for the diaphragm 22 and the shell 17. This additional intermediate layer avoids or at least mitigates failures due to mechanical stress, specifically due to the different coefficients of thermal expansion (comparative). Figure 10 This is caused by ( ).

[0067] According to the present invention, this problem is solved by using materials that are matched with the type of martensitic steel used to manufacture the housing 17, respectively, for manufacturing the partition 22 or the nozzle arc segment 30.

[0068] According to the present invention, the coefficient of thermal expansion of the steel contained in the nozzle arc segment 30 or the steel used to manufacture the nozzle arc segment 30 is substantially equal to the coefficient of thermal expansion of the steel contained in the housing 17 or the steel used to manufacture the housing 17, which is used at least for the support structure of the partition 22 having housing grooves 24, 25. However, the type of steel used for the housing 17 is not suitable for manufacturing the nozzle arc segment 30.

[0069] In one embodiment, the steel used to manufacture the nozzle arc segment 30 is a martensitic steel with higher mechanical strength—specifically, higher tensile strength and / or creep strength—than the martensitic steel used for the housing 17. Preferably, X17CrMoVNbB9-1 (also commonly referred to as "Steel B" or a steel of the St12T type) is used to manufacture the nozzle arc segment 30. In a preferred embodiment, the martensitic steel used to manufacture the nozzle arc segment 30 has a minimum creep strength at a temperature of 580°C. The minimum creep strength of the martensitic steel in the core at 580°C satisfies the condition that the duration until creep rupture occurs is at least 10 MPa under a tensile stress of at least 100 MPa, at least 125 MPa, or at least 150 MPa. 5 Hours. Other steels can also be used to manufacture nozzle arc segment 30, such as X10CrWMoVNb9-2 1.4901, X14CrMoVNbN10-2, 9Cr-3W-3Co-VNbBN or X13CrMoCoVNbNB9-2-1, as long as their coefficient of thermal expansion is substantially equal to that of the shell.

[0070] Figure 10The results show that, at least in the temperature range up to 600°C, the coefficient of thermal expansion of steel B is substantially equal to that of steel Stg9T. Specifically, within this temperature range, the difference between the coefficient of thermal expansion of the shell material and the coefficient of thermal expansion of the nozzle arc segment material is less than 0.05, preferably less than 0.02. Figure 10 As shown.

[0071] In a preferred embodiment, each nozzle segment 30 has a core 37 made of martensitic steel, such as steel B, having minimal creep strength. At least one or more surface areas of each nozzle segment 30 may be covered with a surface coating 38. The surface area of ​​each nozzle segment 30 covered with the surface coating 38 may be the surface of the airfoil 33, such as… Figure 11 and Figure 12 As shown in the diagram. Surface coating 38 can have a uniform thickness ( Figure 11 Or the thickness of the surface coating 38 can vary. Figure 12 In the latter case, the thickness of the surface coating 38 may be greater in the more wear-prone areas of the airfoil 33, specifically in the areas near and at the leading edge, while the surface coating 38 may be thinner in the area at the trailing edge of each airfoil 33. Note that... Figure 11 and Figure 12 The illustrations in the text are for illustrative purposes only and are not to scale.

[0072] The surface coating 38 may comprise at least one of the following: chromium, carbon, and nickel. Preferably, the surface coating 38 comprises at least one of the following: chromium carbide (Cr3C2) and nickel-chromium (NiCr). It can be applied by thermal spraying to at least one corresponding surface area of ​​each nozzle segment 30, and specifically to the surface of the airfoil 33. For example, high-velocity oxygen fuel spraying (HVOF) or high-velocity air fuel spraying (HVAF) can be used. The material of the surface coating 38 may be provided in powder form and sprayed at high speed onto the surface area to be coated by a thermal spraying device.

[0073] Each nozzle segment 30 and the core 37 of each nozzle segment 30 according to this example are made of the same continuous material, specifically steel B, without seams or joints. Therefore, each nozzle segment forms a single integral unit. Preferably, there are no welded joints, adhesive joints, bolted joints, etc., between the airfoil 33 and the first and second ring segments 31, 32. Alternatively, the airfoil 33 of each nozzle segment 30 can be welded or joined to the ring segments 31, 32 in any suitable manner.

[0074] like Figure 4It is evident that, in the axial direction D, the size of the first annular segment 31 can be larger than the size of the second annular segment 32. According to this example, an annular groove 42 is provided on at least one side of the first annular segment 31 facing in the radial direction, and preferably on the side opposite to the axis of rotation A. If the nozzle arc segment 30 is inserted into the first housing groove 24 and the second housing groove 25 of the corresponding housing half 17a or 17b, the protrusion 43 extending from the side wing restricting the first housing groove 24 engages the annular groove 42, as shown. Figure 2 and Figure 7 As best shown in the image. This profile fit can also be used to clamp the nozzle arc segment 30 in the circumferential direction C during assembly, as shown in the reference. Figures 6 to 9 A more detailed explanation.

[0075] Figure 9 This is a flowchart of an embodiment of a method for assembling the diaphragm 22 into the casing 17 of the steam turbine 15.

[0076] In the first step 100, a necessary number of nozzle segments 30, such as eight nozzle segments 30, and two housing halves 17a and 17b are provided. Subsequently, in the second step 101, one of the nozzle segments 30 is inserted into the housing recesses 24, 25 of the first housing half 17a. The inserted nozzle segment 30 is clamped using a clamping element 44 to create a press-fit between the inserted nozzle segment 30 and the first housing half 17a. According to this embodiment, the clamping element 44 has the form of a clamping or braking strip 45, which is used when the nozzle segment 30 moves onto the braking strip 45 or when the braking strip 45 is inserted from one end into the gap between the protrusion 43 and the bottom of the annular recess 42 (compare). Figure 7 When the clamping or braking bar is placed between the bottom of the annular groove 42 and the free end of the protrusion 43, a clamping effect is produced.

[0077] A clamping element 44 can be used to create a press-fit between the first housing half 17a and two directly adjacent nozzle arc segments 30. Specifically, the brake strip 45 forming the clamping element 44 may have one segment located in an annular groove 42 of one nozzle arc segment 30 and another segment extending from the brake strip, such as... Figure 7 As shown in the diagram, the next directly adjacent nozzle segment 30 can be moved onto the accessible section of the brake bar 45 to produce the desired clamping effect. The clamping element 44 or brake bar 45 is used to hold the inserted nozzle segment 30 in the desired position during assembly. They do not need to be removed and can remain in the fully assembled housing 17.

[0078] If it is desired to create a defined gap between two directly adjacent nozzle segments, a gap shim 46 may be placed in the first housing recess 24 in the second step 101. The gap shim 46 may have a plate-like configuration and extend along the intermediate plane S. The two directly adjacent nozzle segments 30 may abut against the gap shim 46 from opposite sides.

[0079] In the third step 102, it is checked whether the first partition segment 22a is complete, that is, whether all the nozzle arc segments 30 forming the first partition segment 22a have been inserted into the housing grooves 24, 25 of the first housing half 17a. If so, the method proceeds to the fourth step 103 (the branch OK from the third step 102). Otherwise, the method repeats the second step 101 again, inserting and clamping the next nozzle arc segment 30 of this first partition segment 22a (the branch NOK from the third step 102).

[0080] In step 103, the two outermost nozzle segments 30 are secured in each case by a retaining element 47 and, according to this embodiment, by a retaining pin 48. The retaining element 47 is press-fitted into a retaining region at the end of the adjacent separating plane P of the first housing groove 24. This retaining region 49 is formed by a housing cavity 50 disposed in the bottom of the first housing groove 24 and an alignment cavity 51 disposed in the first annular segment 31 of the outermost nozzle segment 30. The cavity 51 is open to the side of the first annular segment 31 opposite to the airfoil 33. According to this example, the housing cavity 50 and the cavity 51 define a cross-section orthogonal to the circumferential direction C, which matches the cross-section of the retaining element 47. According to this example, this cross-section is circular.

[0081] The retaining pin 48 is pressed into the opening defined by the mating or aligned cavities 50, 51, resulting in a tight press-fit. Alternatively or otherwise, a material bond may be provided between the retaining pin 48 and the surfaces defining the housing cavity 50 and / or segment cavity 51. This material bond may be achieved by gluing and / or welding.

[0082] In this way, the two outermost nozzle segments 30, positioned directly adjacent to the separation plane P, are fixed in the first housing half 17a. Subsequently, if the gap shims 46 have been inserted between the adjacent nozzle segments, these gap shims 46 can be removed.

[0083] After the retaining pin 48 is inserted, the end portion of the retaining pin 48 can be processed or machined so that it does not extend beyond the end profile defined by the first surface 35 and the adjacent housing surface 52 leading into the housing cavity 50, such as... Figure 8As shown in the example, the end portion of the retaining pin 48 is removed to create a slope with two inclined surface regions, one extending parallel to the first surface 35 and the other extending parallel to the bottom of the first housing recess 24. In this case, the connection between the two partition sections 22a, 22b is not obstructed by the retaining pin 48 that secures the respective outermost nozzle arc segments 30.

[0084] Alternatively, the retaining element 47 or retaining pin 48 may have the necessary shape or profile in its end section before being inserted into the retaining region 49.

[0085] The removal of the gap shim 46 and the treatment of the end section of the retaining pin can be performed during assembly at any time after the outermost nozzle arc 30 has been secured and before the housing halves 17a and 17b are attached together.

[0086] After the first partition segment 22a is assembled in the first housing half 17a, the second partition segment 22b is assembled in the second housing half 17b in a similar manner in steps 104, 105, and 106 of the method. Steps 104 to 106 correspond to steps 101 to 103.

[0087] Finally, after the assembly of the two partition sections 22a and 22b has been completed, the housing halves 17a and 17b are attached to each other in step 8, 107.

[0088] This invention relates to an integral or monolithic nozzle segment 30 having an airfoil 33. According to one aspect of the invention, a steam turbine has a housing 17 supporting a plurality of nozzle segments 30 forming a baffle 22, wherein the airfoil 33 is located in a channel 23 through which the working fluid flows. The baffle 22 is coaxially arranged around the axis of rotation A of the steam turbine 15 and consists of a plurality of individual nozzle segments 30. The nozzle segments 30 and the housing 17 of the steam turbine 15 have substantially equal coefficients of thermal expansion. The housing 17 and the nozzle segments 30 are made of different materials, specifically different types of martensitic steel. According to another aspect of the invention, each nozzle segment 30 has a core 37 comprising martensitic steel having a minimum creep strength at a temperature of 580°C that satisfies the following condition: at least 10 MPa under a tensile stress of at least 100 MPa, at least 125 MPa, or at least 150 MPa. 5 Hour.

[0089] List of reference numerals in the attached diagram:

[0090] 15 Steam Turbine

[0091] 16-axis

[0092] 17. Casing

[0093] 17a First shell half

[0094] 17b Second shell half

[0095] 18 Fixed guide vanes

[0096] 19 Rotating blades

[0097] 20 rotors

[0098] 21. Enter the passage

[0099] 22 partitions

[0100] 23 Fluid connection channel

[0101] 24 First shell groove

[0102] 25 Second shell groove

[0103] 30 Nozzle arc

[0104] 31 First Ring Section

[0105] 32 Second Ring Section

[0106] 33 Airfoil components

[0107] 34 Opening

[0108] 35 First page

[0109] 36 Second page

[0110] 37 core

[0111] 38 Surface coating

[0112] 42 Annular Groove

[0113] 43. Protrusion

[0114] 44 Clamping elements

[0115] 45 Brake Bar

[0116] 46. ​​Gap gasket

[0117] 47 Fixing elements

[0118] 48 Fixed pins

[0119] 49 Fixed Area

[0120] 50. Shell cavity

[0121] 51 segments

[0122] 52. Shell surface

[0123] 100 First Step

[0124] 101 Second Step

[0125] 102 Third Step

[0126] 103 Fourth Step

[0127] 104 Fifth Step

[0128] 105. Step Six

[0129] 106 Seventh Step

[0130] 107 Eighth Step

[0131] α angle

[0132] A. Rotation axis

[0133] C. Circumferential direction

[0134] D Axial Direction

[0135] P Separation plane

[0136] S intermediate plane

Claims

1. A nozzle segment (30) for a diaphragm (22) of a steam turbine (15), wherein the nozzle segment (30) is configured to be attached to the housing (17) of the steam turbine (15), and wherein each nozzle segment (30) includes a first ring segment (31), a second ring segment (32) extending parallel to the first ring segment (31), and a plurality of airfoils (33) extending between the first ring segment (31) and the second ring segment (32). Each nozzle segment (30) has a core (37) comprising martensitic steel, and wherein the coefficient of thermal expansion of each nozzle segment (30) differs from that of the casing (17) of the steam turbine (15) by up to 5% in a temperature range up to 600°C. An annular groove (42) is provided on at least one side of the first annular segment (31) facing in the radial direction. The annular groove (42) is configured to engage a protrusion (43) of the housing (17) extending from the side wing of the first housing groove (24). A clamping element (44) is placed between the bottom of the annular groove (42) and the free end of the protrusion (43) to produce a clamping effect.

2. The nozzle arc segment according to claim 1, wherein the martensitic steel has a minimum creep rupture strength at a temperature of 580°C that satisfies the following condition: at least 10 MPa under a tensile stress of at least 100 MPa, at least 125 MPa, or at least 150 MPa. 5 No breaks within hours.

3. The nozzle arc segment (30) according to claim 1 or 2, wherein the airfoil (33), the first ring segment (31) and the second ring segment (32) are integrally machined from the same solid material workpiece without seams or joints.

4. The nozzle segment according to claim 1 or 2, wherein the airfoil (33), the first ring segment (31) and the second ring segment (32) are individually manufactured and subsequently connected to each other.

5. The nozzle segment according to any one of the preceding claims, wherein each nozzle segment (30) has a core (37) comprising martensitic steel.

6. The nozzle arc segment according to claim 5, wherein the core (37) is made of X17CrMoVNbB9-1.

7. The nozzle segment according to any one of the preceding claims, wherein at least one surface region of the nozzle segment (30) is provided with a surface coating (38), and the surface coating (38) comprises at least one of the group consisting of chromium, carbon and nickel or at least one of the group consisting of titanium, aluminum and nitrogen.

8. The nozzle arc segment according to claim 7, wherein the surface coating (38) comprises at least one of the following: chromium carbide (Cr3C2), nickel chromium (NiCr), and titanium aluminum nitride (TiAlN).

9. The nozzle arc according to claim 7 or 8, wherein the surface coating (38) has resistance such that the material loss of the surface coating disposed within a steam flow at a temperature of 625°C to 650°C is less than 200 micrometers over the predetermined life of the nozzle arc.

10. A steam turbine (15), comprising: - Housing (17), the housing surrounding at least one turbine pressure section connected to the housing (17) to fix guide vanes (18) and rotor blades (19). - A partition (22), the partition being attached to the housing (17) and comprising a plurality of nozzle segments (30), wherein each nozzle segment (30) comprises a first ring segment (31), a second ring segment (32) extending parallel to the first ring segment (31), and a plurality of airfoils (33) extending between the first ring segment (31) and the second ring segment (32), and wherein the coefficient of thermal expansion of each nozzle segment (30) differs from that of the housing (17) of the turbine (15) by at most 0.1% in a temperature range up to 600°C; - An annular groove (42) is provided on at least one side of the first annular segment (31) facing in the radial direction. The annular groove (42) is configured to engage a protrusion (43) of the housing (17) extending from the side wing of the first housing groove (24). A clamping element (44) is placed between the bottom of the annular groove (42) and the free end of the protrusion (43) to produce a clamping effect.

11. The steam turbine according to claim 10, wherein at least the support structure of the casing (17) is made of a material different from that of the nozzle arc segment (30), the support structure supporting the partition (22).

12. The steam turbine according to claim 11, wherein the creep rupture strength of the material of the nozzle arc segment (30) is greater than the creep rupture strength of the material of the support structure of the shell (17).

13. The steam turbine according to any one of claims 10 to 12, wherein the nozzle arc segment (30) is arranged in two opposing housing recesses (24, 25).

14. The steam turbine according to any one of claims 10 to 13, wherein the casing (17) comprises a first casing half (17a) and a second casing half (17b), and wherein a set of nozzle segments (30) attached to the first casing half (17a) forms a first baffle section (22a), and a set of nozzle segments (30) attached to the second casing half (17b) forms a second baffle section (22b).

15. A method for assembling a diaphragm (22) into the casing (17) of a steam turbine (15), the method comprising the steps of: (a) Provides a plurality of integral nozzle segments (30), each integral nozzle segment including a first ring segment (31), a second ring segment (32) extending parallel to the first ring segment (31), and a plurality of airfoils (33) extending between the first ring segment (31) and the second ring segment (32), wherein the coefficient of thermal expansion of each nozzle segment (30) differs from the coefficient of thermal expansion of the casing (17) of the steam turbine (15) by up to 5% in a temperature range up to 600°C; (b) Provide a first housing half (17a) and a second housing half (17b) of an engine housing (17), each having a semi-circular first housing groove (24) and a semi-circular second housing groove (25) arranged opposite to each other. (c) Insert one of the nozzle segments (30) into the first housing groove (24) and the second housing groove (25) in the first housing half (17a), and clamp the inserted nozzle segment (30) by at least one clamping element (44) arranged in one of the housing grooves (24, 25). (d) Repeat step (c) for the other nozzle segments (30) to form a first semi-circular partition segment (22a) from the plurality of nozzle segments (30) in the first housing half (17a). (e) Repeat steps (c) and (d) above for the second housing half (17b) to form a second semi-circular partition section (22b) from the plurality of nozzle arc segments (30) in the second housing half (17b).

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