Turbine system having more failure resistant rotors and repair welding of low alloy ferrous turbine components by controlled weld build-up

Abstract

System for repairing worn surfaces of steam turbine components and especially high pressure turbine rotors, are disclosed. These systems include depositing a first layer of weld metal on a worn surface of the component, whereby a heat-affected zone is created. A second layer of weld metal is then deposited over the first layer using a greater amount of heat to temper at least a portion of the heat-affected zone produced by the first layer. The preferred embodiments include the use of gas tungsten arc welding for providing fine-grain size and more creep resistance, especially in the weld and heat-affected zone. The resulting build-up can be machined, for example into a blade fastening to produce a component having properties equal to or better than the base-metal alloy. The invention also provides a longer lasting turbine system, including rotors which have serrated steeples that are more resistant to failure.

We claim:  
     
       1. In a steam turbine system of the type having a ferrous steam turbine component, said component having a worn surface thereon, the improvement comprising: 
       (a) a first layer of weld metal deposited on said worn surface, said deposition of said first layer producing a heat-affected zone in said component; and  
       (b) a second layer of weld metal deposited to said first layer, said deposition of said second layer tempering at least a portion of said heat-affected zone in said component, wherein said turbine component comprises about 1.05% to 1.35% by weight Cr, about 1.00% to about 1.30% by weight Mo, and about 0.21% to 0.29% by weight V.  
     
     
       2. The system of  claim 1  wherein said turbine component comprises a rotor. 
     
     
       3. The system of  claim 2  wherein said first layer of weld metal comprises a plurality of weld beads disposed transversely across said rotor. 
     
     
       4. The system of  claim 3  wherein said second layer of weld metal comprises a plurality of weld beads disposed transversely across said rotor. 
     
     
       5. The system of  claim 4  further comprising steeples machined from a weld build up comprising at least said first and second layers of weld metal. 
     
     
       6. The system of claim  1   5 wherein at least one of said steeplesteeples has a higher creep resistance than that of the ferrous steam turbine component. 
     
     
       7. The system of  claim 1  wherein said turbine component further comprises greater than  0 . 27 %  by weight C, and less than about  0 . 34   %  C.   
     
     
       8. In a steam turbine system of the type having a ferrous steam turbine component, said component having a worn surface thereon, the improvement comprising: 
       ( a )  a first layer of weld metal deposited on said worn surface, said deposition of said first layer providing a heat - affected zone in said component; and    
       ( b )  a second layer of weld metal deposited above said first layer, said deposition of said second layer tempering at least a portion of said heat - affected zone in said component, wherein said turbine component comprises about  1 . 05   %  to  1 . 35   %  by weight Cr, about  1 . 00   %  to about  1 . 30   %  by weight Mo, about  0 . 21   %  to about  0 . 29   %  by weight V, and greater than  0 . 27   %  C.   
     
     
       9. The system of  claim 8 , wherein said turbine component further comprises less than about  0 . 34 %  by weight C.   
     
     
       10. The system of  claim 8 , wherein said turbine component comprises a rotor. 
     
     
       11. The system of  claim 10 , wherein said rotor is a high pressure rotor. 
     
     
       12. The system of  claim 8 , wherein said first layer of weld metal comprises a plurality of weld beads disposed transversely across said turbine component. 
     
     
       13. The system of  claim 8 , wherein said second layer of weld metal comprises a plurality of weld beads disposed transversely across said turbine component. 
     
     
       14. The system of  claim 12 , further comprising steeples machined from a weld build up comprising at least said layers of weld metal. 
     
     
       15. The system of  claim 14 , wherein at least one of said steeples has a higher creep resistance than a creep resistance of said turbine component. 
     
     
       16. The system of  claim 8 , wherein said worn surface includes high temperature properties that are improved compared to high temperature properties of a base metal of the turbine component. 
     
     
       17. The system of  claim 16 , wherein the high temperature properties include creep and fatigue properties. 
     
     
       18. The system of  claim 8 , wherein said worn surface is substantially free of weld porosity, cracking, and lack of fusion.