Patent ID: 6129514
Filing Date: 2000-10-10
Classification: C22C,F01D

Abstract:
A low pressure steam turbine including a rotor shaft, rotating blades planted in said rotor shaft, stationary blades for guiding flow of steam to said rotating blades, and an inner casing for holding said stationary blades, characterized in thatsaid rotating blades have a double-flow structure in which two sets, each being composed of five stages or more of said rotating blades, are symmetrically disposed right and left, and a first stage one of said rotating blades is planted at a central portion of said rotor shaft;said rotor shaft is made from a Ni--Cr--Mo--V based low alloy steel containing Cr in an amount of 1 to 2.5 wt % and Ni in an amount of 3.0 to 4.5 wt %, said rotor shaft being specified such that a distance (L) between centers of bearings provided for said rotor shaft is 6500 mm or more, the minimum diameter (D) of portions, of said rotor shaft, corresponding to said stationary blades is 750 mm or more, and the ratio (L/D) is in a range of 7.2 to 10.0; anda final stage one of said rotating blades is made from a high strength martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N, said final stage rotating blade being specified such that a value of [the length of a blade (inch).times.the number of revolution (rpm)] is 125,000 or more.