Double flow turbine with axial adjustment and replaceable steam paths and methods of assembly

In a double-flow steam turbine having an axis, first-stage rotors spaced axially one from the other, a reheat tub disposed between said first-stage rotors and including first and second arcuate diaphragms axially spaced one from the other and disposed about said turbine axis, each said diaphragm having an outer ring, an inner ring and a plurality of nozzles circumferentially spaced one from the other about said axis and between said outer and inner rings whereby the nozzles of said axially spaced diaphragms define steam paths in generally axially opposite directions relative to one another, said nozzles having trailing edges spaced a predetermined axial distance from said rotors, and an inner annulus disposed about said axis and extending axially between said inner rings of said axially spaced diaphragms;

• the improvement wherein said first and second diaphragms each comprise arcuate diaphragm segments, means for establishing a spacing between trailing edges of the nozzles of said segments and said rotors greater than said predetermined axial distance while maintaining the axial distance between said rotors constant, said arcuate diaphragm segments each including a portion of said outer ring, a patch ring secured on a downstream side of said outer ring portion and having an axial extent substantially the same as the difference between said predetermined axial distance and said greater spacing for accommodating said greater spacing.

In a double-flow steam turbine having first-stage rotors and a damaged double-flow reheat tub including a pair of axially spaced diaphragms and an inner annulus spanning between said diaphragms, a method of retrofitting a reheat tub with increased setback of diaphragms relative to the first-stage rotors comprising the steps of:

• removing the damaged reheat tub from the turbine;
• providing a reheat tub with increased setback having at least three discrete parts including (i) first and second arcuate diaphragm segments each having inner and outer ring portions, a plurality of circumferentially spaced nozzles therebetween, and hook portions on said inner ring portions and (ii) an inner annular segment having at opposite ends hook portions generally complementary to the hook portions of said inner ring portions;
• and
• assembling said reheat tub with increased setback of said nozzles relative to the respective axially adjacent first-stage rotors by relatively rotating said diaphragms and said annular segment to engage the respective hook portions thereof thereby to secure said diaphragm segments and said inner segment one to the other with said diaphragm segments spaced axially one from the other along said inner segment.