Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Specific casing or vane material
Reexamination Certificate
2001-11-14
2004-06-29
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Specific casing or vane material
C416S24100B
Reexamination Certificate
active
06755613
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on and hereby claims priority to European Application No. 991096272 filed on May 14, 2001, and PCT Application No. PCT/EP00/04319 filed on May 12, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention relates to a component, in particular a component which can be exposed to hot vapor, having a metallic base body which has a protective coating in order to increase the resistance of the base material to oxidation. The invention also relates to a process for producing a protective coating in order to increase the resistance to oxidation on a component which can be exposed to hot vapor, having a metallic base body which has a base material.
In various technical fields, components are exposed to hot vapor, in particular steam. This applies, for example, to components used in steam installations, in particular in steam power plants. With a view to increasing the efficiency of steam power plants, the efficiency is increased, inter alia, by raising the steam parameters (pressure and temperature). Future developments will involve pressures of up to 300 bar and temperatures of up to over 650° C. To produce elevated steam parameters of this level, there is a need for suitable materials with a high creep strength at elevated temperatures.
Since austenitic steels, on account of unfavorable physical properties, such as a high coefficient of thermal expansion and low thermal conductivity, in this case meet their limits, numerous variants of ferritic-martensitic steels with a high creep strength and chromium contents of from 9% by weight to 12% by weight are currently being developed.
EP 0 379 699 A1 has disclosed a process for increasing the resistance of a blade of a thermal machine, in particular a blade of an axial compressor, to corrosion and oxidation.
The base material of the compressor blade in this case is formed of a ferritic-martensitic material. A securely adhered surface-protection layer comprising 6 to 15% by weight of silicon, remainder aluminum, is sprayed onto the base material using the high-speed method with a particle velocity of at least 300 m/s onto the surface of the base material. A conventional paint-spraying process is used to apply a plastic, for example polytetrafluoroethylene, to this metal protective layer, which plastic forms the covering layer (outer layer) of the blade. The process provides a protective layer on a blade which has an increased resistance to corrosion and erosion in the presence of steam and at relatively moderate temperatures (450° C.), as are relevant to compressor blades.
The article “Werkstoffkonzept für hochbeanspruchte Dampfturbinen-Bauteile”, by Christina Berger and Jürgen Ewald in Siemens Power Journal April 1994, pp. 14-21, has provided an analysis of the materials properties of forged and cast chromium steels. The creep strength of chromium steels containing 2 to 12% by weight of chromium and additions of molybdenum, tungsten, niobium and vanadium decreases continuously as the temperature rises. For use at temperatures of over 550 to 600° C., forged shafts are described, which contain from 10 to 12% by weight of chromium, 1% of molybdenum, 0.5 to 0.75% by weight of nickel, 0.2 to 0.3% by weight of vanadium, 0.12 to 0.23% by weight of carbon and optionally 1% by weight of tungsten. Castings produced from chromium steel are used in valves for a steam turbine, outer and inner casings of high-pressure, medium-pressure, low-pressure and saturated-steam turbines. For valves and casings which are exposed to temperatures of 550 to 600° C., steels which contain 10 to 12% by weight of chromium are used, and these steels may in addition contain 0.12 to 0.22% by weight of carbon, 0.65 to 1% by weight of manganese, 1 to 1.1% by weight of molybdenum, 0.7 to 0.85% by weight of nickel, 0.2 to 0.3% by weight of vanadium or also 0.5 to 1% by weight of tungsten.
The article “Steam Turbine Materials: High Temperature Forgings” by C. Berger et al., 5
th
Int. Conf. Materials for Advanced Power Engineering, Liege, Belgium, Oct. 3-6, 1994, provides a summary of the development of CrMoV steels which contain from 9 to 12% by weight of chromium and have a high creep strength. These steels are in this case used in steam power installations, such as conventional steam power plants and nuclear power plants. Components produced from chromium steels of this type are, for example, turbine shafts, casings, bolts, turbine blades, pipelines, turbine-wheel disks and pressure vessels. A further summary of the development of new materials, in particular 9-12% by weight chromium steels, is given by the article “Material development for high temperature-stressed components of turbomachines” by T. -U. Kern et al. in Stainless Steel World, October 1998, pp. 19-27.
Further application examples for chromium steels containing 9% by weight to 13% by weight of chromium are given, for example, in U.S. Pat. No. 3,767,390. The martensitic steel used in this document is employed for steam-turbine blades and the bolts which hold together the casing halves of a steam turbine.
EP 0 639 691 A1 has disclosed a turbine shaft for a steam turbine which contains 8 to 13% by weight of chromium, 0.05 to 0.3% by weight of carbon, less than 1% of silicon, less than 1% of manganese, less than 2% of nickel, 0.1 to 0.5% by weight of vanadium, 0.5 to 5% by weight of tungsten, 0.025 to 0.1% by weight of nitrogen, up to 1.5% by weight of molybdenum, and also between 0.03 and 0.25% by weight of niobium or 0.03 and 0.5% by weight of tantalum or less than 3% by weight of rhenium, less than 5% by weight of cobalt, less than 0.05% by weight of boron, with a martensitic structure.
WO 91/08071 relates to a protective layer protecting against corrosive and erosive attack at a temperature of up to approximately 500° C. for a substrate formed of a chromium steel. A protective layer which contains aluminum is formed on the substrate. The aluminum-containing protective layer is applied electrochemically, in particular by electrodeposition, and is hardened or age-hardened at least on its surface in order to form the protective layer. As a result, a so-called duplex layer is formed, which comprises the metal layer and the hard layer.
SUMMARY OF THE INVENTION
It is an object of one aspect of the invention to provide a component which can be exposed to hot vapor, having a metallic base body, which has an increased resistance to oxidation compared to the metallic base body. A further possible object of the invention is to describe a process for producing a protective coating in order to increase the resistance to oxidation of the base material on a component.
According to one aspect of the invention, the object relating to a component is achieved by the fact that the component has a protective layer, which has a thickness of less than 50 &mgr;m and contains aluminum, on the base material.
One aspect of the invention is based on the discovery that, when a base material is used at elevated temperatures, for example in steam power plants, as well as a high creep strength a considerable resistance to oxidation in the steam is also necessary. The oxidation of the base materials in some cases increases considerably as the temperature rises. This oxidation problem is intensified by the reduction in the chromium content of the steels used, since chromium as an alloying element has a positive influence on the resistance to scaling. Therefore, a lower chromium content can increase the rate of scaling. By way of example, in the case of steam generator tubes, thick oxidation layers on the steam side may lead to a deterioration in the heat transfer from the metallic base material to the steam and therefore to the temperature of the pipe wall rising and to the service life of the steam-generator pipes being reduced. In steam turbines, by way of example jamming of screw connections and valves caused by scaling and an additional load caused by the growth of scale in blade grooves, or flaking of scale at blade outlet e
Edgar Richard A.
Siemens Aktiengesellschaft
Staas & Halsey , LLP
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