Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Plural rigidly related blade sets
Reexamination Certificate
2000-10-20
2002-12-31
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Plural rigidly related blade sets
C415S200000
Reexamination Certificate
active
06499946
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a steam turbine rotor having a connection structure for application to a steam turbine plant that includes in combination at least two of a high pressure steam turbine, an intermediate steam turbine and a low pressure steam turbine, and also relates to a method of manufacturing the steam turbine rotor.
In a typical steam turbine plant equipped with a high pressure steam turbine, an intermediate pressure steam turbine and a low pressure steam turbine, a material (metal material) of a steam turbine rotor incorporated into each turbine is selected depending on the steam conditions used, e.g., pressure, temperature, flow rate, etc. The steam turbine rotor for use in the high pressure steam turbine and intermediate steam turbine having the steam temperature of 550° C. to 600° C. can be made of e.g., 1%CrMoV steel (ASTM-A470, class 8) or 12%Cr steel (Japanese Patent Pub. No. SHO 60-54385). The steam turbine rotor for use in the low pressure steam turbine having the steam temperature equal to or higher than 400° C. can be made of, e.g., NiCrMo steel (ASTM-A471, classes 2 to 7) containing 2.5% or more Ni.
In a recent steam turbine plant directed toward a larger capacity and a higher efficiency, due to the necessity for each turbine of a reduced size and weight and of a simple structure, a lot of attention is being paid to the appearance of so-called high-low pressure integrated, high-intermediate-low pressure integrated, or intermediate-low pressure integrated steam turbine rotors integrated into one piece and using the same metal material for each steam turbine including the high pressure steam turbine to the low pressure steam turbine.
Such a one-piece steam turbine rotor needs a sufficient high-temperature creep rupture strength on its high pressure high temperature side and needs a sufficient tensile strength, yield strength and toughness on its low pressure/low temperature side. This means that a single rotary shaft (rotor) requires different mechanical characteristics. Specifically, the metals used in the commercial machines are 1%CrMoVNiNb steel (e.g., Japanese Patent Pub. No. SHO 58-13608), 1.7%Ni2.25%CrMoVWNb steel (e.g., Japanese Patent Laid-open Pub. No. HEI 7-316721), etc.
Although the above described one-piece steam turbine rotors is integrally molded from the initial step of fabrication, previously separately fabricated high, intermediate and low pressure steam turbine rotors may be joined together by bolts (e.g., Japanese Patent Laid-open Pub. No. SHO 62-189301) or may be welded together.
The steam turbine rotor having the welded structure is classified into two types depending on the step to weld each steam turbine rotor. One is obtained by the welding in the process of the steam turbine rotor manufacturing steps and the other is obtained by the mutual welding after the completion of manufacture of each steam turbine rotor.
For the manufacture of the former, a plurality of ingots are roughly forged, welded together and then finish forged, which is disclosed in e.g., Japanese Patent Laid-open Pub. No. SHO 53-147653.
For the manufacture of the latter, the steam turbine rotors formed from dissimilar metal of different components and compositions are welded together, which is disclosed in e.g., Japanese Patent Laid-open Pub. No. SHO 57-176305.
It has hitherto been common for the high pressure, intermediate pressure and low pressure steam turbine rotors to provide a disk-structure (in which the steam turbine rotors each has an sliced disk shape so that they are laid one on top of the other) for the welded connection thereof. In this case, the steam turbine rotors formed from the same metal of the same components and compositions are welded and connected without welding the ones made of the dissimilar metal of different components and compositions.
Use of ESR (electroslag remelting) process is proposed as the other connection method to be effected during the steam turbine rotor manufacturing steps.
This connection method can include some approaches, i.e., immediately after the electroslag melting of one consumable electrode, the other consumable electrode may be subjected to the electroslag melting, with the resultant two parts being joined together for integral molding (e.g., Japanese Patent Pub. No. SHO 53-42446), a plurality of ingots of different components and compositions may be connected together for being remelted as the ESR electrode (e.g., Japanese Patent Pub. No. SHO 56-14842), or with a view to reducing the pool depth at the center, hollow electrodes may be connected together for ESR (e.g., Japanese Patent Laid-open Pub. No. HEI 6-155001).
In this manner, a number of connection means have been disclosed for the conventional steam turbine rotors, and some of them have been adopted for the commercial machines.
The recent steam turbine plant has a trend toward enhancement on the reduced size and weight as well as the simplified structure, and from this viewpoint, investigation is directed to the high-low pressure, high-intermediate-low pressure or intermediate-low pressure steam turbine rotors.
The conventional steam turbine rotors are formed from metals of components and compositions which have been developed in conformity with the steam conditions such as the steam temperature and pressure of the individual steam turbines, i.e., high pressure, high-intermediate pressure, intermediate pressure and low pressure steam turbines. Thus, intact application of those metals of the components and compositions to the high-low pressure, high-intermediate-low pressure and intermediate-low pressure steam turbines would pose deficiencies which follow.
(1) The 1%CrMoV rotor has a good performance in the creep rupture strength within the high-temperature region of the order of 550° C., although it may not necessarily present a sufficient tensile strength and toughness within the low temperature region and may possibly undergo a ductile fracture, a brittle fracture, etc. As the prevention measures against those, it is necessary to reduce the stress which may occur at the low-pressure part of the steam turbine rotor. However, the reduction of the stress occurring at the low-pressure part may restrict the length of the turbine blades disposed at the turbine stages, to consequently make it difficult to enhance the power plant capability.
In spite of its excellent high-temperature creep rupture strength, it would be insufficient for the higher temperature (approx. 600° C. ) and higher pressure steam at the turbine inlet, which is required to achieve an improved efficiency in the recent power plant.
(2) The 12%Cr rotor could satisfy the above turbine inlet steam conditions due to its superior characteristics in the high temperature creep rupture strength to the 1%CrMoV steel rotor, but it presents an insufficient toughness. As a countermeasure against this fact, the length of the turbine blades disposed at the low pressure turbine stages is restricted, in the same manner as the case of the 1%CrMoV rotor.
(3) The NiCrMoV steel rotor is advantageous in the tensile strength and toughness within the low temperature region, but it may fail to present a sufficient creep rupture strength therewithin. Thus, its use in the high pressure steam turbine or intermediate pressure steam turbine may restrict the rise of the steam temperature at the turbine inlet due to its insufficient strength, making it difficult for the power plant to achieve an improved efficiency.
In this manner, when attempting to impart the increased capacity and higher efficiency to the steam turbine plant, especially, by use of the high temperature and high pressure steam with the turbine blade of a larger length incorporated therein, many restrictions have been imposed on the conventional high-low, high-intermediate-low and intermediate-low pressure integrated steam turbine rotors formed from the same material (metal material) such as the heat resisting steel.
Nevertheless, small-sized steam turbines with a small power output have used high-low, high-intermediate-l
Asai Satoru
Inukai Takao
Ishii Ryuichi
Kaneko Joji
Kikuchi Masataka
Kabushiki Kaisha Toshiba
Look Edward K.
White Dwayne
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