Turbine diaphragm construction

Abstract

A turbine diaphragm has radially inner and outer hollow diaphragm rings ( 22, 24 ) comprising box structures that include the radially inner and outer platform portions ( 261, 262 ) of static blade units ( 26 ) as part of their structures. The box structures are strengthened by the incorporation of ribs or struts ( 28, 30 ) which extend radially and axially between the walls of the box structures.

1 . A high or intermediate pressure, axial flow, turbine diaphragm ( 20 ) comprising a radially inner ring and a radially outer ring ( 22 ,  24 ), at least one such ring being hollow and having axially opposed walls ( 221 ,  222  and/or  241 ,  242 ) comprising plate material. 
     
     
         2 . A turbine diaphragm according to  claim 1 , comprising:
 (a) an annulus of static blade units ( 26 ), each such blade unit having an aerofoil portion ( 263 ), a radially inner platform portion ( 261 ) and a radially outer platform portion ( 262 ); and   (b) a radially inner hollow diaphragm ring ( 22 ) and/or a radially outer hollow diaphragm ring ( 24 ), the or each such hollow ring comprising a box structure that includes the blade units ( 26 ) as part of the box structure.   
     
     
         3 . A turbine diaphragm according to  claim 2 , in which a box structure of the inner hollow diaphragm ring ( 22 ) comprises:
 (a) a pair of axially opposed side walls ( 221 ,  222 );   (b) a radially inner circumferentially extending wall ( 223 ); and   (c) a radially outer circumferentially extending wall formed by the radially inner platform portions ( 261 ) of the static blade units ( 26 ).   
     
     
         4 . A turbine diaphragm according to  claim 2 , in which a box structure of the outer hollow diaphragm ring ( 24 ) comprises:
 (a) a pair of axially opposed side walls ( 241 ,  242 );   (b) a radially outer circumferentially extending wall ( 243 ); and   (c) a radially inner circumferentially extending wall formed by the radially outer platform portions ( 262 ) of the static blade units ( 26 ).   
     
     
         5 . A turbine diaphragm according to  claim 2 , in which one or both of the radially inner and outer platform portions ( 261 ,  262 ) of the static blade units are formed integrally with the aerofoil portion ( 263 ). 
     
     
         6 . A turbine diaphragm according to  claim 2 , in which the box structure of the or each hollow diaphragm ring ( 22 ,  24 ) is strengthened by incorporating a plurality of reinforcing ribs ( 28 ,  30 ) into the box structure, the ribs being aligned to the radial and axial directions and circumferentially spaced-apart from each other. 
     
     
         7 . A turbine diaphragm according to  claim 6 , in which the radially outer wall ( 243 ) of the outer diaphragm ring ( 24 ) is divided into separate circumferentially extending sections by at least one of the reinforcing ribs ( 30 ). 
     
     
         8 . A turbine diaphragm according to  claim 3 , in which the radially inner side of the radially inner wall ( 223 ) of the radially inner ring ( 22 ) comprises a circumferentially extending recess ( 228 ) configured to retain a seal against leakage between relatively high and low pressure sides of the diaphragm ( 20 ). 
     
     
         9 . A turbine diaphragm according to  claim 1 , in which to enable assembly of the diaphragm ( 20 ) within a turbine, the diaphragm is fabricated as two halves which upon assembly are united with each other on a diametric joint line (J). 
     
     
         10 . A turbine diaphragm according to  claim 9 , in which a bolted joint is provided at each end of the diametric joint line (J) of the outer diaphragm ring. 
     
     
         11 . A turbine diaphragm according to  claim 9 , in which diametrically opposed ends of the upper and lower halves of the diaphragm are held in registration with each other by location features that support them within a surrounding turbine casing. 
     
     
         12 . A turbine diaphragm according to  claim 1 , in which only one of the inner and outer diaphragm rings is a hollow structure, the other ring being solid. 
     
     
         13 . A method of fabricating the turbine diaphragm of  claim 6  in which a box structure of the inner hollow diaphragm ring ( 22 ) comprises:
 (a) a pair of axially opposed side walls ( 221 ,  222 ); 
 (b) a radially inner circumferentially extending wall ( 223 ); and 
 (c) a radially outer circumferentially extending wall formed by the radially inner platform portions ( 261 ) of the static blade units ( 26 ), and 
 in which the inner hollow diaphragm ring ( 22 ) is fabricated by the steps of: 
 (a) attaching the side walls ( 221 ,  222 ) to the reinforcing ribs ( 28 ); 
 (b) attaching the inner platforms ( 261 ) of the blade units ( 26 ) to the side walls ( 221 ,  222 ) of the inner ring ( 22 ); and 
 (c) attaching the inner circumferentially extending wall ( 223 ) to the side walls of the inner ring ( 22 ). 
 
     
     
         14 . A method of fabricating the turbine diaphragm of  claim 6  in which a box structure of the outer hollow diaphragm ring ( 24 ) comprises:
 (a) a pair of axially opposed side walls ( 241 ,  242 ); 
 (b) a radially outer circumferentially extending wall ( 243 ); and 
 (c) a radially inner circumferentially extending wall formed by the radially outer platform portions ( 262 ) of the static blade units ( 26 ), and 
 in which the outer hollow diaphragm ring ( 24 ) is fabricated by the steps of: 
 (a) attaching the side walls ( 241 ,  242 ) to the reinforcing ribs ( 30 ); 
 (b) attaching the outer platforms ( 262 ) of the blade units ( 26 ) to the side walls ( 241 ,  242 ) of the outer ring ( 24 ); 
 (c) attaching the outer circumferentially extending wall ( 243 ) to the side walls of the outer ring ( 24 ). 
 
     
     
         15 . A method of fabricating the turbine diaphragm of  claim 6  in which a box structure of the inner hollow diaphragm ring ( 22 ) comprises:
 (a) a pair of axially opposed side walls ( 221 ,  222 ); 
 (b) a radially inner circumferentially extending wall ( 223 ); and 
 (c) a radially outer circumferentially extending wall formed by the radially inner platform portions ( 261 ) of the static blade units ( 26 ), and in which a box structure of the outer hollow diaphragm ring ( 24 ) comprises: 
 (a) a pair of axially opposed side walls ( 241 ,  242 ); 
 (b) a radially outer circumferentially extending wall ( 243 ); and 
 (c) a radially inner circumferentially extending wall formed by the radially outer platform portions ( 262 ) of the static blade units ( 26 ), the method comprising the steps of: 
 (a) attaching the side walls ( 221 ,  222 ) and ( 241 ,  242 ) to the reinforcing ribs ( 28 ) and ( 30 ); 
 (b) attaching the inner platforms ( 261 ) of the blade units ( 26 ) to the side walls ( 221 ,  222 ) of the inner ring ( 22 ); 
 (c) attaching the side walls ( 241 ,  242 ) of the outer ring ( 24 ) to the outer platforms ( 262 ) of the blade units ( 26 ); 
 (d) attaching the inner circumferentially extending wall ( 223 ) to the side walls of the inner ring ( 22 ) and attaching the outer circumferentially extending wall ( 243 ) to the side walls of the outer ring ( 24 ). 
 
     
     
         16 . A variation of the method of  claim 13 , in which the radially inner wall ( 223 ) is attached to the inner ring ( 22 ) before the inner platforms ( 261 ) of blade units ( 26 ) are attached to the inner ring ( 24 ). 
     
     
         17 . A variation of the method of  claim 14 , in which the radially outer wall ( 243 ) is attached to the outer ring ( 24 ) before the side walls ( 241 ,  242 ) of the outer ring ( 24 ) are attached to the outer platforms ( 262 ) of blade units ( 26 ). 
     
     
         18 . A variation of the method of  claim 15 , in which the radially inner wall ( 223 ) is attached to the inner ring ( 22 ) before the inner platforms ( 261 ) of blade units ( 26 ) are attached to the inner ring ( 24 ). 
     
     
         19 . A variation of the method of  claim 15 , in which the radially outer wall ( 243 ) is attached to the outer ring ( 24 ) before the side walls ( 241 ,  242 ) of the outer ring ( 24 ) are attached to the outer platforms ( 262 ) of blade units ( 26 ).