EP1181437B1 - Steam turbine component and method for producing a protective coating on the component - Google Patents

Abstract

The invention relates to a component (80) which can be subjected to hot steam and which has a metallic base body (81) to which a protective layer (82) is bonded by diffusion. Said protective layer (82) increases the base material's resistance to oxidation, comprises aluminum, and has a thickness (D) of less than 50 νm. The invention also relates to a method for producing a protective coating which increases the component's (80) resistance to oxidation.

Description

The invention relates to a steam turbine component, in particular a steam turbine component that can be exposed to hot steam, with a metallic base body of a protective coating to increase the oxidation resistance of the base material having. The invention further relates to a method for Production of a protective coating to increase the resistance to oxidation on a steam turbine component, which is exposed to hot steam, with a metallic base body, which has a base material.

In various technical fields, steam turbine components are used exposed to hot steam, especially water vapor. This applies, for example, to steam turbine components Steam plants, especially in steam power plants. As part of The increase in efficiency of steam power plants is under by increasing the steam parameters (pressure and temperature) achieved an increase in efficiency. future Developments are pressures up to 300 bar and temperatures up to over 650 ° C. To realize such elevated Steam parameters are suitable materials with high Strength in the creep range required at elevated temperatures.

Because austenitic steels due to unfavorable physical Properties such as high thermal expansion coefficient and lower Thermal conductivity, will reach their limits here, are currently different variants of creep resistance, ferritic-martensitic steels with chrome contents of 9% by weight to 12% by weight developed.

EP 0 379 699 A1 describes a method for increasing the Corrosion and oxidation resistance of a blade thermal machine, especially a compressor blade an axial compressor. The basic material of the compressor blade consists of a ferritic-martensitic Material. A solid is placed on the base material adhesive surface protective layer consisting of 6 to 15 % By weight silicon, rest aluminum according to the high-speed process with a particle velocity of at least 300 mls sprayed onto the surface of the base material. This metal protective layer is made according to a conventional one Paint spraying process a plastic, for example polytetrafluoroethylene, applied which plastic the top layer (outer layer) of the blade. With the procedure a protective layer is provided on a blade which increased resistance to corrosion and erosion when present of water vapor and comparatively moderate temperatures (450 ° C), as relevant for compressor blades are.

In the article "Material concept for highly stressed steam turbine components", by Christina Berger and Jürgen Ewald in Siemens Power Journal 4/94, pp. 14-21, were the material properties for forged and cast chrome steels examined. The creep rupture strength of chrome steels with 2 to 12% by weight of chromium and additions of molybdenum, tungsten, Niobium and vanadium decrease with increasing temperature continuously. For use at temperatures from Forged shafts are indicated above 550 to 600 ° C a proportion of 10 to 12 wt.% Chromium, 1% molybdenum, 0.5 to 0.75 wt% nickel, 0.2 to 0.3 wt% vanadium, 0.12 to 0.23 % By weight carbon and optionally 1% by weight tungsten. Made of chrome steel Cast parts are used in valves a steam turbine, outer and inner casing of high pressure, Medium pressure, low pressure and saturated steam turbines. For valves and housings at temperatures from 550 to 600 ° C find 10 to Steels containing 12% by weight of chromium, the addition 0.12 up to 0.22% by weight carbon, 0.65 to 1% manganese, 1 to 1.1% Molybdenum, 0.7 to 0.85% nickel, 0.2 to 0.3% by weight vanadium or can also contain 0.5 to 1% by weight of tungsten.

In the article "Steam Turbine Materials: High Temperature Forgings" by C. Berger et al, 5 ^th Int. Conf. Materials for Advanced Power Engineering, Liége, Belgium, Oct. 3-6, 1994, gives an overview of the development of creep resistant CrMoV steels containing 9 to 12% by weight chromium. These steels are used in steam power plants such as conventional steam power plants and nuclear power plants. Components made from such chrome steels are, for example, turbine shafts, housings, bolts, turbine blades, pipelines, turbine wheel disks and pressure vessels. The article "Material development for high temperature-stressed components of turbomachines" by T.-U. provides a further overview of the development of new materials, especially 9-12% by weight chromium steels. Kern et al in Stainless Steel World, Oct. 1998, pp. 19-27.

Further application examples of chrome steels with 9% by weight to 13% by weight of chromium is given, for example, in US Pat. No. 3,767,390. The martensitic steel used herein finds Use with steam turbine blades and the housing halves a steam turbine holding bolts together.

EP 0 639 691 A1 describes a turbine shaft for a steam turbine indicated the 8 to 13 wt.% Chromium, 0.05 to 0.3 % By weight carbon, less than 1% silicon, less than 1% manganese, less than 2% nickel, 0.1 to 0.5% by weight vanadium, 0.5 to 5 % By weight tungsten, 0.025 to 0.1% by weight nitrogen to 1.5% by weight Molybdenum, and between 0.03 to 0.25% by weight of niobium or 0.03 up to 0.5% by weight tantalum or less than 3% by weight rhenium, less than 5 % Cobalt, less than 0.05% boron with a martensitic structure having.

Achieving protection against a corrosive and erosive Attack at a temperature up to about 500 ° C for one Chromium steel existing substrate, with a Protective layer is formed, which contains aluminum described in WO 94/08071.

The object of the invention is a steam turbine component, which hot steam is exposed to a metallic Specify basic body, which one compared to the metallic Base body has increased resistance to oxidation. Another object of the invention is to provide a method for Production of a protective coating to increase the resistance to oxidation of the base material on a steam turbine component specify.

According to the invention, the object is directed to a component solved in that the steam turbine component with a metallic Base body made of a base material to which one Protective layer to increase the oxidation resistance of the Base material, which protective layer is a aluminum-enriched zone facing the base body in the form of an intermetallic connection between aluminum and the base material and the outer surface forms, which is subjected to hot steam during operation of the steam turbine is, the protective layer having a thickness of less than 20 µm and the proportion of aluminum in the protective layer above Is 50% by weight.

The invention is based on the knowledge that at high operating temperatures of a base material, for example in steam power plants in addition to increased creep rupture strength also an increased requirement for resistance to oxidation in the steam is required. The oxidation of the Base materials increase with increasing temperature Part clearly too. This problem of oxidation is caused by the Lowering the chromium content in those used Steels are tightened because chrome is an alloying element has a positive impact on scale resistance. With A lower chromium content can therefore lead to an increase the tinder speed come. For example, at Steam generator tubes through thick layers of oxidation on the Steam side to a deterioration of the heat transfer from metallic base material for steam and thus for a temperature increase the pipe wall and to reduce the service life of the steam generator pipes come. With steam turbines could it for example for scaling screw connections and valves as well as additional stress caused by scale growth in shovel grooves or by flaking of scale Blade leading edges come to increase the notch stress.

Due to a negative influence on the mechanical properties the possibility of the base material Resistance to scaling by changing the alloy composition of the base material through elements reduced in scale such as chrome, aluminum and / or silicon in an increased concentration out. With the invention, however, which is a thin has an aluminum-enriched zone of the base material, will already increase the resistance to oxidation of the base material by up to an order of magnitude. Furthermore, steam turbine components which have been machined in this way can can be easily protected by using a receive such an oxidation coating. Because of the low The thickness of the protective layer also has no negative influence of the base material in its mechanical properties instead of. The protective layer is too big Part, possibly completely through the diffusion of aluminum in the base material or vice versa. A corresponding Diffusion of the aluminum into the base material into and from elements of the base material in an aluminum layer inside, as part of a heat treatment below the tempering temperature of the base material take place, so that no new heat treatment of the steam turbine component is required. If necessary, such a diffusion also when using the component with those who are there Temperatures take place. As a result of the metallic bond between the aluminum and the alloying elements of the base material high adhesive strength is achieved. moreover the protective layer has a high hardness, so that also a high abrasion resistance is given. Furthermore can form a particularly uniform layer thickness the protective layer even in inaccessible places simple application processes can be achieved.

The thickness of the protective layer is preferably below 10 µm. It can preferably be between 5 and 10 μm.

In addition to aluminum, the protective layer preferably also has Iron and chrome on, these can for example be from one Base material diffused into the protective layer or with an aluminum-containing layer on the base material have been applied. Furthermore, the protective layer in addition to aluminum, silicon, in particular up to 20% by weight exhibit. By adding silicon accordingly can be the hardness of the protective layer as well as other mechanical Properties can be set specifically.

The base material of the steam turbine component is preferred a chrome steel. This can be between 0.5% and 2.5% by weight. Chromium and also between 8% and 12% by weight of chromium, in particular have between 9 wt% and about 10 wt% chromium. In addition to chrome, such a chrome steel, manganese between 0.1 to 1.0, preferably 0.45% by weight. He can too Carbon between 0.05 and 0.25% by weight, silicon smaller 0.6, preferably about 0.1% by weight; Molybdenum between 0.5 to 2 % By weight, preferably about 1% by weight; Nickel up to 1.5% by weight, preferably 0.74% by weight; Vanadium between 0.1 and 0.5% by weight, preferably about 0.18% by weight; Tungsten between 0.5 to 2 % By weight, preferably 0.8% by weight; Niobium up to 0.5% by weight, preferably about 0.045% by weight; Nitrogen less than 0.1% by weight, preferably about 0.05% by weight and optionally an additive of boron less than 0.1% by weight, preferably about 0.05% by weight.

The base material is preferably martensitic, ferritic-martensitic or ferritic.

The steam turbine component with the thin protective layer is preferably a component of a steam turbine or a Component of a steam generator, in particular a steam generator tube. The steam turbine component can be a forged part or be a casting. The steam turbine component can be a Turbine blade, a valve, a turbine shaft, a wheel disc a turbine shaft, a connecting element like one Screw, a bolt, a nut etc., a housing component (Inner housing, guide vane carrier, outer housing), one Pipeline or the like.

The on a process of making a protective coating to increase the oxidation resistance on a component, what hot steam can be exposed to, directed task is solved in that on a metallic base body, which has a base material, one less than 20 µm thick aluminum-containing layer is applied and the steam turbine component at a temperature that is below the tempering temperature of the base material is held, so that a reaction of the aluminum with the base material for formation an aluminum-containing protective layer takes place, wherein in the protective layer facing the base body form of an intermetallic enriched with aluminum Connection between aluminum and the base material is formed, the proportion of aluminum in the protective layer is over 50% by weight.

The aluminum-containing layer is preferred here to carry out the diffusion at a temperature in the range the melting temperature of aluminum, especially between Kept at 650 ° C and 720 ° C. The temperature can also lie lower. Diffusion may also be used during the use of the component in a steam system the operating temperature then prevailing there.

The component will carry out the appropriate temperature the reaction for at least 5 minutes, preferably over 15 Min., If necessary also exposed for a few hours.

The layer containing the aluminum is preferably with a thickness, in particular average thickness, between 5 microns and 30 microns, especially between 10 microns and 20 microns applied. The application of the thin aluminum-containing or aluminum-containing For example, an inorganic layer is used High temperature paint. The layer can be sprayed on be applied, which means that even in inaccessible Provide an appropriate protective coating on the component is achievable. A heat treatment of the component for Carrying out the reaction between base material and coating can, for example, in the oven or by others suitable sources of heat. After heat treatment the applied aluminum pigment-containing layer can be a substantially closed, about 5 to 10 microns thick Fe-Al-Cr-containing protective layer, i.e. in the form of a intermetallic connection between aluminum and the Base metal. By applying the layer on a chrome steel becomes a significant improvement in scaling behavior of the base material. Due to a high aluminum content, especially of over 50 wt.%, in the by reaction of the aluminum pigments with the base material Protective layer, in particular a diffusion layer the oxidation resistance of the component is significantly increased. The the resulting protective layer is extremely hard (Vickers hardness HV) of about 1200, for example.

Such a thin aluminum-containing layer can alternatively also be applied by an adapted immersion aluminizing process. The change in the dip aluminizing process is carried out in such a way that, in contrast to the usual aluminum-containing layer thicknesses of between 20 and 400 μm, a corresponding reduction in the layer thickness is achieved. Aluminum hot-dip layers produced by the hot-dip process form several phases with iron (eta phase / Fe ₂ Al ₅ ; zeta phase / FeAl ₂ , teta phase / FeAl ₃ ). In conventional hot dipping (fire aluminizing) for simple steel parts, appropriately pretreated components to be coated are immersed in molten aluminum or aluminum alloy baths at temperatures from 650 ° C to 800 ° C and removed again after a dwell time of 5 to 60 seconds. An intermetallic protective layer and an aluminum cover layer are formed on it. However, these coatings, which are produced with conventional fire aluminizing, have the danger that aluminum is introduced into the water vapor circuit through the application of aluminum, which could cause undesirable side effects such as poorly soluble aluminum silicate deposits.

FIG 1

eine schematische Darstellung einer Dampfkraftanlage,

FIG 2

einen schematischen Schnitt durch eine Dampfturbinenanordnung, und

FIG 3

ein Schliffbild durch eine aluminiumhaltige Schutzschicht.

The method and the component having the protective layer are explained in more detail using the exemplary embodiments shown in the drawing. Some of them show schematically and not to scale:

FIG. 1

a schematic representation of a steam power plant,

FIG 2

a schematic section through a steam turbine assembly, and

FIG 3

a micrograph through an aluminum-containing protective layer.

1 shows a steam power plant 1 with a steam turbine plant 1b. The steam turbine system 1b comprises a steam turbine 20 with coupled generator 22 and in one of the Steam turbine 20 assigned water-steam circuit 24 a the steam turbine 20 downstream condenser 26 and a steam generator 30. The steam generator 30 is a waste heat continuous steam generator executed and is with hot exhaust gas applied to a gas turbine 1a. The steam generator 30 can alternatively also as a steam generator fired as coal, oil, wood etc. be executed. The steam generator 30 has a variety from tubes 27 in which the steam for the steam turbine 20 is generated and a protective layer 82 (see FIG. 3) may have to protect against oxidation. The steam turbine 20 consists of a high-pressure part turbine 20a, one Medium pressure part turbine 20b and a low pressure part turbine 20c, the generator 22 drive.

The gas turbine 1 a comprises a turbine 2 with a coupling Air compressor 4 and one of the turbine 2 upstream Combustion chamber 6, which is connected to a fresh air line 8 of the air compressor 4 is connected. In the combustion chamber 6 of the turbine 2 opens a fuel line 10. The turbine 2 and the air compressor 4 and a generator 12 sit on one common shaft 14. For feeding in the gas turbine 2 relaxed working fluid AM or flue gas is an exhaust pipe 34 to an input 30a of the once-through steam generator 30 connected. The relaxed working medium AM (hot gas) Gas turbine 2 leaves the once-through steam generator 30 via the latter Exit 30b towards a not shown Stack.

The condenser 26 connected downstream of the steam turbine 20 via a condensate line 35 into which a condensate pump 36 is connected to a feed water tank 38. The feed water tank 38 is on the output side via a Main feed water line 40 into which a feed water pump 42 is connected, with one arranged in the continuous steam generator 30 Economizer or high pressure preheater 44 connected. The High-pressure preheater 44 is on the output side to one for one Continuous-flow evaporator 46 connected. The Evaporator 46 is in turn on the output side via a steam line 48, in which a water separator 50 is connected a superheater 52 connected. In other words: the Water separator 50 is between the evaporator 46 and the Superheater 52 switched.

The superheater 52 is on the output side via a steam line 53 with the steam inlet 54 of the high pressure part 20a of the steam turbine 20 connected. The vapor outlet 56 of the high pressure part 20a of the steam turbine 20 is via a reheater 58 to the steam inlet 60 of the medium pressure part 20b of the steam turbine 20 connected. Its steam outlet 62 is via a Overflow line 64 with the steam inlet 66 of the low pressure part 20c of the steam turbine 20 connected. The steam outlet 68 of the low pressure part 20c of the steam turbine 20 is via a Steam line 70 connected to the condenser 26, so that a closed water-steam circuit 24 is created.

On the one connected between the evaporator 46 and the superheater 52 Water separator 50 is a suction line 72 for separated water W connected. In addition, the Water separator 50 a drain line that can be shut off with a valve 73 74 connected. The suction line 72 is on the output side connected to a jet pump 75, the primary side with from the water-steam circuit 24 of the steam turbine 20 removed medium can be acted upon. The jet pump 75 is on the primary side on the output side also to the water-steam cycle 24 connected. The jet pump 75 is in an input side with the steam line 53 and thus with connected to the outlet of the superheater 52 via a valve 76 lockable steam line 78 switched. The steam pipe 78 opens on the output side into a steam outlet 56 of the High pressure part 20a of the steam turbine 20 with the reheater 58 connecting steam line 90. In the embodiment According to Figure 1, the jet pump 75 is thus from the water-steam cycle 24 removed steam D as a blowing agent operated. Depending on the requirements, components of the steam power plant can 1b with an aluminum-containing protective layer be less than 50 µm thick (see FIG. 3).

In Figure 2 is a section in a schematic longitudinal section through a steam turbine plant with one along a turbine shaft 101 extending axis of rotation 102. The turbine shaft 101 is made up of two sub-turbine shafts 101a and 101b put together in the area of the camp 129b are firmly connected. The steam turbine plant has a high-pressure turbine section 123 and a medium-pressure turbine section 125 each with an inner housing 121 and one this enclosing outer housing 122. The high pressure turbine 123 is designed as a pot. The medium pressure turbine 125 is double flow. It is also possible that the medium-pressure turbine section 125 single-flow is executed. Along the axis of rotation 102 is between the high pressure turbine section 123 and the medium pressure turbine section 125, a bearing 129b is arranged, the turbine shaft 101 in bearing 129b has a storage area 132. The turbine shaft 101 is on a further bearing 129a next to the high-pressure part turbine 123 stored. In the area of this camp 129a, the high-pressure turbine section 123 has a shaft seal 124 on. The turbine shaft 101 is opposite the outer housing 122 of the medium-pressure turbine section 125 through two further shaft seals 124 sealed. Between a high pressure steam inflow area 127 and a steam outlet area 116 has the turbine shaft 101 in the high-pressure sub-turbine 123 Blades 113 on. Axial in the flow direction of the steam each row of blades 113 is a row of guide vanes 130 upstream. The medium pressure turbine section 125 has a central steam inflow region 115. the The turbine shaft is assigned to the steam inflow region 115 101 a radially symmetrical shaft shield 109, a cover plate on the one hand to divide the steam flow in the two floods of the medium-pressure turbine section 125 and on the other hand to prevent direct contact of the hot steam with the turbine shaft 101 is used. The turbine shaft 101 has 125 medium-pressure guide vanes in the medium-pressure turbine section 131 and medium pressure blades 114 on. The one from the medium-pressure turbine section 125 from an outflow connection 126 escaping steam reaches one of these downstream low-pressure turbine, not shown.

3 shows a section of a longitudinal section through a near-surface area of a steam turbine component 80, a component of a steam turbine plant, such as a steam generator tube 27, a turbine shaft 101, an outer turbine housing 122, an inner housing 121 (guide vane carrier), a shaft shield 109, a valve or similar. The steam turbine component 80 has one Base material 81, for example a chrome steel with 9 to 12% by weight of chromium and possibly further alloying elements such as Molybdenum, vanadium, carbon, silicon, tungsten, manganese, Niobium and a rest of iron. The base material 81 goes in a protective layer 82 over, the aluminum up to over 50 % By weight. The average thickness D of the protective layer 82 is about 10 µm. The section shown is a thousand times microscopic magnification. The base material 81 has a Vickers hardness of about 300 and the protective layer a Vickers hardness of about 1200. Through the Protective layer 82 becomes the oxidation resistance and thus the scale resistance of the steam turbine component 80, also at high steam temperatures of up to over 650 ° C, significantly increased, what the life of the steam turbine component 80 at Use in a steam turbine plant or use in Steam exposure significantly increased at over 600 ° C. The metallic protective layer 82 also forms the outer Surface (cover layer) of the protective layer 82 Steam turbine component 80. The outer surface of the Protective layer 82 is included in the operation of the steam turbine system hot steam.

Claims (12)

1. Steam turbine component (80) having a metallic parent body (81) of a parent material, on which parent body (81) a protective coating (82) for increasing the oxidation resistance of the parent material is integrally bonded, which protective coating (82) has a zone facing the parent body (81) and enriched with aluminium and in the form of an intermetallic compound between aluminium and the parent material and forms the outer surface, to which live steam is admitted during operation of the steam turbine, the protective coating (82) having a thickness (D) of below 20 µm, and the proportion of aluminium in the protective coating (82) being over 50% by weight.
2. Steam turbine component (80) according to Claim 1, in which the thickness (D) of the protective coating (82) is below 10 µm.
3. Steam turbine component (80) according to Claim 1 or 2, in which the thickness (D) of the protective coating (82) is between 5 µm and 10 µm.
4. Steam turbine component (80) according to one of Claims 1 to 3, in which the protective coating (82), in addition to aluminium, also has iron and chromium.
5. Steam turbine component (80) according to one of the preceding claims, in which the protective coating (82), in addition to aluminium, also has silicon, in particular up to 20% by weight.
6. Steam turbine component (80) according to one of the preceding claims, in which the parent material is a chromium steel.
7. Steam turbine component (80) according to Claim 6, in which the chromium steel has between 0.5% by weight and 2.5% by weight of chromium or between 8% by weight and 12% by weight of chromium, in particular between 9% by weight [lacuna].
8. Steam turbine component (80) according to Claim 6 or 7, in which the parent material (81) is martensitic, ferritic/martensitic or ferritic.
9. Steam turbine component (80) according to one of the preceding claims, which is a forged part or a cast part.
10. Steam turbine component (10 [sic]) according to Claim 9, which is a turbine blade (113, 114), a valve (76), a turbine shaft (101, 32), a wheel disc of a turbine shaft, a connecting element such as a screw, a casing component, a pipeline (70, 64) or the like.
11. Steam turbine component (80) according to one of the preceding claims, which is a component of a steam generator (30), in particular a steam generator tube (27).
12. Method of producing a protective coating for increasing the oxidation resistance on a steam turbine component (80) which can be exposed to live steam, having a metallic parent body (81) which has a parent material, in which case

    a) a coating (82) containing aluminium and having a thickness of below 20 µm is applied, and

    b) the steam turbine component (80) is kept at a predetermined temperature which lies below the annealing temperature of the parent material for the reaction of the protective coating (82) containing aluminium with the parent material (81), so that a zone which faces the parent body (81), is enriched with aluminium and is in the form of an intermetallic compound between aluminium and the parent material is formed in the protective coating (82), the proportion of aluminium in the protective coating (82) being over 50% by weight.

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