Patent Document

BACKGROUND OF THE INVENTION 
       [0001]    Exemplary embodiments of the invention relate to the art of turbomachines and, more particularly, to a method of refurbishing a seal land on a turbomachine turbine transition piece. 
         [0002]    In general, turbomachines, particularly gas turbine engines, combust a fuel/air mixture to release heat energy to form a high temperature gas stream that is channeled to a turbine section via a hot gas path. More specifically, a compressor compresses incoming air to a high pressure. The high pressure air is delivered to a combustion chamber to mix with fuel and form a combustible mixture. The combustible mixture is then ignited to form a high pressure, high velocity gas that is passed through a transition piece into a first stage of a turbine. The turbine converts thermal energy from the high temperature, high velocity gas stream to mechanical energy that rotates a turbine shaft. The turbine shaft is coupled to and drives the compressor and also other machinery such as an electrical generator. 
         [0003]    In a typical gas turbine, an air duct surrounds the transition piece and delivers cooling air from the compressor. Joints between the transition piece and the turbine must be properly sealed. That is, the combustion process creates a pressure differential between the hot gases passing into the turbine and the cooling air supplied by the compressor. Without proper sealing between the transition piece and the turbine, compressor cooling air could pass into the turbine resulting in performance and efficiently losses. The seal must be able to withstand the high temperatures of the engine while at the same time remaining flexible so as to accommodate vibrations/deflections and/or travel of the transition piece due to thermal expansion and turbine starts and stops. Over time, the vibrations/deflections and/or travel cause the seal to abrade a seal land portion of the transition piece resulting in wear. When the wear is significant, the seal land must be refurbished. 
         [0004]    At present, many turbines are taken off line every 12,000 or so hours of run time or combustion intervals (CI) in order to perform inspection/routine maintenance. During the CI, seal lands are inspected and, if out of tolerance, refurbished. Currently, a seal land is refurbished by applying a new layer of material on the seal land. The new layer of material, typically a nickel based alloy similar to that used in the construction of the transition pieces, is applied in layers by a welding process. While the new layer of material enables the transition piece to return to service, the new layer will erode as fast as, or faster, than the original seal land. Moreover, there are a finite number of refurbishing cycles that can be performed before the seal land will become fatigued. Refurbishing a seal land in this manner is very expensive, requiring up to 300 hours/set, and only extends the life of a transition piece a finite period. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    In accordance with an exemplary embodiment of the invention, a method of refurbishing a seal land on a transition piece of a turbomachine includes removing the transition piece from the turbomachine, applying a wear strip to a well surface of the seal land, and covering the wear strip with a slot protector. 
         [0006]    In accordance with another exemplary embodiment of the present invention, a refurbished transition piece for a turbomachine includes a main body having a first end that extends to a second end through an intermediate portion. A seal land extends about a portion of at least one of the first and second ends. The seal land includes first and second opposing side walls that are joined by a third wall to collectively define a slot. A wear strip is bonded to at least one of the first, second and third walls, and a slot protector is bonded to the wear strip. The slot protector provides abrasion resistance to the seal land. 
         [0007]    The above described exemplary embodiments result in enhanced operating efficiencies for turbomachines. That is, the wear strips provide additional wear resistance for the seal land thereby increasing an overall service life of the transition piece. More specifically, by adding a slot protector on the seal land, repeated welding steps previously required to provide renewed wear protection are eliminated. Eliminating welding steps also reduces any thermal cycling, which, over time, will weaken the seal land. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a right plan view of a turbomachine transition piece having a refurbished seal land in accordance with an exemplary embodiment of the invention; 
           [0009]      FIG. 2  is a partial, cross-sectional side view of a refurbished seal land in accordance with an exemplary embodiment of the invention; 
           [0010]      FIG. 3  is a partial cross-sectional side view illustrating a first step of refurbishing a seal land in accordance with an exemplary embodiment of the invention; 
           [0011]      FIG. 4  is a partial cross-sectional side view of the seal land of  FIG. 4  after attachment of a wear strip; 
           [0012]      FIG. 5  is a partial cross-sectional side view of the seal land of  FIG. 4  after attachment of a slot protector; and 
           [0013]      FIG. 6  is a partial cross-sectional side view of a refurbished seal land having a slot protector and an outer wear insert in accordance with another exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    With initial reference to  FIG. 1 , a transition piece (TP) for a turbomachine, for example a gas turbine engine, is indicated generally at  2 . Transition piece  2  is operatively connected between a turbine combustor portion (not shown) and a first turbine stage  4 . Towards that end, transition piece  2  includes a main body  8  having a first end  10  that extends to a second end  12  through an intermediate portion  14 . In accordance with one aspect of the exemplary embodiment, transition piece  2  is formed from a nickel-based alloy such as, but not limited to, NIMONIC® 263. In the exemplary embodiment shown, first end  10  of transition piece  2  is supported upon the gas turbine by a forward mount  20  while second end  12  connects to first turbine stage  4  through a picture frame or seal land  40  establishing a turbine interface (not separately labeled). 
         [0015]    As best shown in  FIG. 2 , seal land  40  includes a first side wall  50  having a first surface  51 , a second surface  52  and a third or connecting surface  53 . Seal land  40  further includes a second side wall  56  having a first surface  57 , a second surface  58  and a third or connecting surface  59 . Finally, seal land  40  is shown to include a third wall  62  that connects first and second walls  50  and  56  so as to define a slot  70 . As shown, seal land  40  provides an interface between transition piece  2  and first turbine stage  4 . That is, first turbine stage  4  is provided with a seal element  80  that operatably engages seal land  40  in order to prevent hot gases passing through transition piece  2  from escaping or leaking from the turbine interface. 
         [0016]    In the exemplary embodiment shown, seal element  80  includes a first leg portion  82 , a second leg portion  83  and a retaining portion  84 . Retaining portion  84  includes a clip section  86  that retains a seal cloth  90  in a desired orientation. That is, seal cloth  90  extends into slot  70  and engages with first wall  50  to establish a seal between transition piece  2  and first turbine stage  4 . Seal cloth  90  is preferably formed from a cobalt based alloy, such as, but not limited to, L-605 or L-606, and is flexible so as to enable movement between transition piece  2  and first turbine stage  4  while, at the same time, preventing hot gases from escaping. However, over time, and through a number of combustion intervals, seal cloth  90  will abrade first sidewall  50  creating wear which, if left unchecked, may result in leakage of hot gas from transition piece  2 . Towards that end, the seal land  40  must be repaired in order to minimize wear and eliminate potential leak paths. 
         [0017]    Reference will now be made to  FIGS. 3 through 5  in describing an exemplary method of repairing seal land  40 . Initially, transition piece  2  is removed from the gas turbine exposing seal land  40 . At this point, first surface  51  is blended to an even thickness so as to have a width of approximately 0.190 inches. After establishing a uniform thickness for slot  70 , a wear strip  100  is bonded to first surface  51  of first side wall  50 . Wear strip  100  is preferably made from the same material as transition piece  2 , e.g., a nickel based alloy such as, but not limited to, NIMONIC®  263 , and is welded to first surface  51 . Wear strip  100 , when properly positioned within slot  70  creates a thickness of between approximately 0.160 inches (4.064 mm) and 0.190-inches (4.826 mm). After attaching wear strip  100 , a slot protector  104  is installed. Slot protector  104  is bonded to wear strip  100  so as to restore blueprint dimensions for seal land  40 . That is, in accordance with one aspect of the exemplary embodiment, slot protector  104  has a thickness of approximately 0.030-inches (0.762 mm) so as to restore slot  70  to approximately blueprint dimensions such as, a thickness of between approximately 0.190-inches (4.826 mm) and 0.220-inches (5.588 mm). Slot protector  104  in accordance with one aspect of the invention is formed from a cobalt-based alloy such as, but not limited to, L-605 or L-606, and is stitch welded to wear strip  100 . By forming slot protector  104  from the same material as seal cloth  90 , e.g., L-605 or L-606, additional wear resistance is provided for seal land  40  such that abrasions or other forms of wear are substantially eliminated. 
         [0018]    Reference will now be made to  FIG. 6  in describing a slot protector  114  constructed in accordance with a second embodiment of the present invention. As shown, slot protector  114  is S-shaped and secured to first surface  51  of first sidewall  50 . More specifically, slot protector  114  includes a first end  116  that extends across third wall  62  to an intermediate section  117  that runs along first surface  51  before terminating at a second end  118  that extends across a portion of third surface  53 . With this arrangement, slot protector  114  not only protects first surface  51  of seal land  40  but also outer surfaces of third wall  62  and third surface  53 . 
         [0019]    In further accordance with the exemplary embodiment shown, seal land  40  includes an outer wear insert  125  mounted to second surface  52  of first sidewall  50 . More specifically, while forming slot  70  so as to have a substantially uniform thickness, a recess  130  is formed in second surface  52  and a chamfer  132  is provided at third surface  53 . With this arrangement, outer wear insert  125  is secured to second surface  52  to provide additional wear characteristics between second leg portion  83  of seal element  80  and transition piece  2 . That is, outer wear insert  125  includes a first section  138  that extends along second surface  52  to a curved section  139  before terminating in a third section  140  that extends along third surface  53 . Outer wear insert  125  is, in accordance with an exemplary embodiment herementioned, formed from a cobalt based alloy such as, but not limited to, L-605 or L-606. With this arrangement, slot protector  114  and outer wear insert  125  provide additional wear resistance for seal land  40  increasing an overall service life of transition piece  2 . That is, by adding a slot protector to seal land  40 , repeated welding steps to attach the wear strip are eliminated thereby also eliminating thermal cycling which, over time, will weaken seal land  40 . The further addition of an outer wear insert serves to even further enhance the overall service life of transition piece  2 . 
         [0020]    In general, this written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of exemplary embodiments of the present invention if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Technology Category: 4