Titanium steam turbine blades

Abstract

ABSTRACT The use of titanium alloys for the long last stage and L-1 stage of low-pressure steam turbines has been in development for over 30 years, and appears to be entering commercial use. The titanium blades are used in the steam transition L-1 row, because they are immune to pitting corrosion by the corrosive early condensates at the Wilson line. In the last stage row, lighter titanium blades permit longer blade length and larger exit annulus areas than 12Cr steel blades. The last row can be designed to increase the thermal efficiency by 1-2% or the power by about 50%, reducing the number of steam flows by one-third to one-half. A disadvantage of titanium alloys is their low damping capacity, which requires blade designs that maximize mechanical and aerodynamic damping. The water droplet erosion resistance of titanium alloys is sufficient not to require protection in the L-1 row, but the last stage rows operating at supersonic tip speeds require the use of erosion shields.