Page 106 - Steam Turbines Design, Applications, and Rerating

Rotors for Impulse Turbines 87

Figure 4.7 Integrally shrouded blading used in special applica-
tions. (Dresser-Rand Company, Wellsville, N.Y.)

Each wheel is preceded and followed onto the shaft by a heated ring
that shrinks into a previously machined shrink ring groove in the shaft
to provide positive axial positioning of the wheel.
The shaft material for built-up rotor construction for engineered tur-
bines is usually per ASTM A293, Cl. 3, a chrome-molybdenum-nickel
alloy steel. The forging is purchased with a proper heat stability test
per the requirements of ASTM A293. The commercial specification for
these materials is given in Table 4.1.

TABLE 4.1 Typical Materials of Construction for Multistage Mechanical Drive
Steam Turbines
Material Commercial specifications
Steam chest and casing
600 psi—750°F/41 bar— Cast carbon steel ASTM A-216 Grade WCB
399°C
600 psi—825°F/41 bar— Carbon-molybdenum ASTM A-217 Grade WC1
440°C steel
900 psi—900°F/62 bar— Chromium-molybdenum ASTM A-217 Grade WC6
482°C steel
2000 psi—950°F/138 bar— Chromium-molybdenum ASTM A-217 Grade WC9
510°C steel
Exhaust casing
Condensing and High-strength cast iron ASTM A-278 Class 40
Non-Condensing (Cast)