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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 31 Schematic arrangement <strong>of</strong> stationary and rotating blades.<br />

1.8070) [8]. LP rotors are mostly typically constructed <strong>of</strong> NiMoV or<br />

NiCrMoV materials, particularly 3.5 NiCrMoV. Shrunk-on disks, when<br />

used, are made from forgings <strong>of</strong> similar NiCrMoV materials, conforming to<br />

ASTM A294 Grade B or C, or ASTM 471, Classes 1 to 3.<br />

Nuclear rotors. Nuclear HP rotors are also typically manufactured out <strong>of</strong><br />

NiCrMoV materials.<br />

Rotor Damage Mechanisms<br />

Fossil HP and IP rotors. Damage mechanisms include creep, low cycle<br />

fatigue (thermal mechanical), creep-fatigue interactions, fatigue from<br />

rotating weight (‘‘self-bending’’), and embrittlement. Key areas <strong>of</strong> concern<br />

in the HP rotors <strong>of</strong> fossil fired units are the accumulation <strong>of</strong> damage at the<br />

bore and in other areas <strong>of</strong> stress concentration resulting from cyclic loading<br />

and elevated temperature operation. Stress concentrations <strong>of</strong> concern are<br />

bores, keyways, heat and seal grooves, locking slots, ventilation holes, fillets,<br />

and the blade attachments—tangential entry, triple pin, and axial fir-tree<br />

designs.<br />

Early development <strong>of</strong> rotor forgings concentrated on heat treating the<br />

rotor to give maximum creep resistance. The material was austenitized at<br />

1010 8C (1850 8F). This high creep strength was accompanied by poor creep<br />

Copyright © 2003 Marcel Dekker, Inc.

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