Highly corrosion-resistant movable blade assembly for a steam turbine, in particular a geothermal impulse turbine

Abstract

A highly corrosion-resistant movable blade assembly ( 20 ) for a steam turbine, in particular a geothermal impulse turbine, has an array ( 14 ) of rotor blades ( 15 ) carried by a shaft ( 7 ) rotating about an axis (A)/each blade ( 15 ) extends between one end ( 22 ) attached to the shaft ( 7 ), and a free end ( 24 ) terminating with a top portion ( 25 ) with no mechanical connection to the top portions ( 25 ) of the other blades ( 15 ); the blades ( 15 ) are made of a nickel-based metal alloy containing chromium, iron, niobium, and molybdenum, e.g. a metal alloy in the INCONEL® group or a similar material. For high resistance against corrosion and erosion. In particular, the blades are unshrouded to avoid accumulation of deposits and subdeposit corrosion.

1 . A highly corrosion-resistant movable blade assembly ( 20 ) for a steam turbine, in particular a geothermal impulse turbine, comprising an array ( 14 ) of rotor blades ( 15 ) carried by a shaft ( 7 ) rotating about an axis (A); the assembly being characterized in that each blade ( 15 ) extends between one end ( 22 ) attached to the shaft ( 7 ), and a free end ( 24 ) terminating with a top portion ( 25 ) with no mechanical connection to the top portions ( 25 ) of the other blades ( 15 ); and in that the blades ( 15 ) are made of a nickel-based metal alloy. 
     
     
         2 . An assembly as claimed in  claim 1 , characterized in that the blades ( 15 ) are made of a nickel-based metal alloy containing chromium, iron, niobium, and molybdenum. 
     
     
         3 . An assembly as claimed in  claim 1 , characterized in that the metal alloy contains over roughly 45% by weight of nickel, and over roughly 15% by weight of chromium. 
     
     
         4 . An assembly as claimed in  claim 1 , characterized in that the metal alloy contains over roughly 3% by weight of niobium, and over roughly 2% by weight of molybdenum. 
     
     
         5 . An assembly as claimed in  claim 1 , characterized in that the metal alloy contains significant quantities of iron, niobium, and molybdenum, together with smaller quantities of aluminium aluminum and titanium. 
     
     
         6 . An assembly as claimed in  claim 5 , characterized in that the metal alloy contains roughly 0.1 to 1% by weight of aluminum, and roughly 0.5 to 1.5% by weight of titanium. 
     
     
         7 . An assembly as claimed in  claim 1 , characterized in that the metal alloy is a nickel-based alloy in the INCONEL® group or a similar material. 
     
     
         8 . A steam turbine ( 1 ), in particular a geothermal impulse turbine, comprising a stator ( 5 ), and a rotor ( 6 ) connected integrally to a shaft ( 7 ) rotating about a rotation axis (A); the turbine being characterized in that the rotor ( 6 ) comprises a movable blade assembly ( 20 ) as claimed in  claim 1 .