Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Specific casing or vane material
Reexamination Certificate
2002-03-22
2003-06-10
Nguyen, Ninh H. (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
06575700
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel steam turbine blade and, more particularly to a low pressure steam turbine having rotor blades in the final stage of the low pressure steam turbine made of a 12% Cr group steel and a steam turbine power plant using the low pressure steam turbine.
At the present time, 12Cr—Mo—Ni—V—N steel is used for steam turbine rotor blades. In recent years, it is required from the viewpoint of energy conservation to improve the thermal efficiency of a stream turbine, and it is required from the viewpoint of space conservation to make the components compact.
Employing long-length steam turbine blades is an effective means for improving the thermal efficiency of a steam turbine and for making the components compact. Therefore, the length of low pressure steam turbine blades in the final stage is being lengthened year by year. This trend makes the use condition of the steam turbine blades severer, and accordingly a higher strength material is required because the strength of the 12Cr—Mo—Ni—V—N steel is insufficient. As the strength of a material for the long blade, a high tensile strength of basic mechanical property is required.
Further, the material is required to be high in strength and high in toughness from the viewpoint of securing safety against rupture.
As structural materials having a tensile strength higher than that of the conventional 12Cr—Mo—Ni—V—N steel (a martensite group steel), Ni based alloys and Co base alloys are generally known. However, they are not suitable for the blade material because they are worse in hot workability, in cutting workability and in vibration damping characteristic.
WO97/30272 discloses a rotor blade in the final stage of a low pressure steam turbine made of a 12% Cr group martensite steel, and a low pressure steam turbine using the turbine blades and a steam turbine power plant using the low pressure steam turbine. Further, a low pressure turbine blade having a 48-inch blade length made of 17-4PH steel for a 3000 rpm turbine is described in Technical Report of Mitsubishi Heavy Industry, Vol. 35, No. 1 (January, 1998).
Rotor blades in the final stage of the low pressure steam turbine having a blade length of 43 inches for a 3000 rpm turbine and a blade length of 35.8 inches for a 3600 rpm turbine are described in WO97/30272. However, there is no description on a length of the blade longer than the above, and there is no description on shape of the blade nor size of the low pressure steam turbine either.
Further, the above-mentioned technical report does not describe on any remedy for a longer blade nor on strength and toughness of the 17-4PH steel.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a steam turbine blade made of a martensite steel having high strength and high toughness which is capable of attaining a blade length above 48 inches for a 3000 rpm turbine and above 40 inches for a 3600 rpm turbine, and a low pressure steam turbine and a steam turbine power generating plant using the steam turbine blades.
The present invention is characterized by a steam turbine blade having a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, which is made of a martensite steel having a 20° C. V-notch impact value larger than 6 kg·m/cm
2
and a 20° C. tensile strength larger than 140 kg/mm
2
, preferably larger than 150 kg/mm
2
, further preferably larger than 152 kg/mm
2
. For the latter tensile strengths, 20° C. V-notch impact values are preferably larger than 5 kg·m/cm
2
and larger than 6 kg·m/cm
2
, respectively.
The present invention is a steam turbine blade made of a martensite steel having a 20° C. V-notch impact value, wherein said 20° C. V-notch impact value is larger than a value (y) (kg·m/cm
2
) calculated by an equation y=−0.44x+68, preferably y=−0.44x+71, further preferably y=−0.44x+72, where (x) is a 20° C. tensile strength (kg/mm
2
).
It is preferable that the steam turbine blade described above is made of a martensite steel containing C of 0.13-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; Mo of 1.5-4%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35; and N of 0.04-0.15%, on the basis of weight.
The present invention is characterized by a steam turbine blade, which is made of a martensite steel containing C of 0.19-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; Mo of 1.5-4%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35; and N of 0.04-0.15%, on the basis of weight.
The steam turbine blade described above is characterized by that the matensite steel contains C of 0.25-0.40% and Mo of 1.5-2.0%; or C of 0.19-0.40% and Mo of 3-4%, on the basis of weight.
The present invention is characterized by a steam turbine blade having a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, which is made of a martensite steel containing C of 0.16-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35%; and N of 0.04-0.15%, on the basis of weight.
The present invention is characterized by a steam turbine blade having a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, which is made of a martensite steel containing C of 0.13-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35%; and N of 0.04-0.15%, on the basis of weight, wherein a combination of the amount of C and the amount of Mo falls within a range formed by connecting to points A (0.21%, 1.5%), B (0.15%, 2.5%), C (0.15%, 3.2%) and D (0.25%, 4.0%). Further, it is preferable that the combination of the amount of C and the amount of Mo falls within a range formed by connecting to points E (0.39%, 1.9%), F (0.21%, 2.4%) and G (0.25%, 3.90%).
The present invention is characterized by a steam turbine power generating plant comprising a high pressure turbine, an intermediate pressure turbine and one or two low pressure turbines connected in tandem or cross, wherein blades in a final stage of the low pressure turbine are the steam turbine blades described in any one of the above items.
The present invention is characterized by a steam turbine power generating plant comprising a set of a high pressure turbine and a low pressure turbine and a generator; and a set of an intermediate pressure turbine and a low pressure turbine and a generator, the sets being connected in tandem or cross, wherein blades in a final stage of the low pressure turbines are the steam turbine blades described in any one of the above items.
The present invention is characterized by a low pressure steam turbine comprising a rotor shaft; rotor blades mounted on the rotor shaft; fixed blades for guiding flow of steam to the rotor blades; and a casing holding the fixed blades, wherein the rotor blades in a final stage are the steam turbine blades described in any one of the above items.
The present invention is characterized by a low pressure steam turbine having a rotating speed of 3000 rpm or 3600 rpm, which comprises five stages of the rotor blades symmetrically arranged in both sides, and is of a double flow construction having the rotor blades in the first stages being mounted in a middle portions of the rotor shaft, and the rotor blades in the final stages are the steam turbine blades described in any one of the above items.
It is preferable that the rotor shaft is made of a bainite steel having a 0.02% yield strength at room temperature above 80 kg/mm
2
in the central portion of the rotor shaft; 0.2% yield strength above 87.5 kg/mm
2
or a tensile strength above 92 kg/mm
2
; and a FATT below −5° C. or a 20° C. V-notch impact value above 10 kg·m.
It is preferable that the bainite steel is a forged steel containing C of 0.20-0.28%; Si less tha
Arai Masahiko
Nakamura Shigeyoshi
Onoda Takeshi
Shiga Masao
Mattingly Stanger & Malur, P.C.
Nguyen Ninh H.
LandOfFree
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