Page 100 - Steam Turbines--Design, Applications, and Rerating by Heinz-Bloch, Murari-Singh

Chapter
4

Rotors for Impulse Turbines

Although rotors for impulse steam turbines exhibit great variety in
physical size, wheel diameter, number of wheels and other construction
features, they may all be conveniently classified in one of three basic
categories:

1. Built-up rotors: Those rotors that are constructed by shrinking the
wheels onto a shaft (Fig. 4.1)
2. Solid rotors: Those rotors in which the wheels and shaft are
machined from a single, integral forging (Fig. 4.2)
3. Combination solid and built-up rotors: Those rotors in which some
of the wheels are integral with the shaft and some are shrunk on
(Fig. 4.3)

There are several factors that determine the type of construction that
is utilized for any particular turbine rotor application. The most signif-
icant of these factors are:

1. Long-term operating experience
2. Pitch diameter
3. Maximum operating speed
4. Steam temperature

4.1 Long-Term Operating Experience
This selection factor is often influenced by user preferences based on
maintainability criteria or design conservatism. An applicable Ameri-
can Petroleum Institute Specification (API 612) states:

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