Abstract:
Aspects of the present invention relate to systems and method for fabricating a combustor end cover where the cover does not include braze joints within the cover. The combustor cover provides a configuration and method of manufacturing where all fuel and air annuli can be placed within the cover without requiring use of brazed inserts, which were previously known to crack and leak.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/939,456 filed on Feb. 13, 2014. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention generally relates to a fuel system for a gas turbine combustor, and more specifically to an end cover that supplies fuel and air to the fuel nozzles of the combustor. 
       BACKGROUND OF THE INVENTION 
       [0003]    In a typical gas turbine engine, a compressor having alternating stages of rotating and stationary airfoils is coupled to a turbine, which also has alternating stages of rotating and stationary airfoils. The compressor stages decrease in size, and as the volume of each stage of the compressor decreases, the air passing therethrough is compressed, raising its temperature and pressure. The compressed air is then supplied to one or more combustors which mixes the air with fuel and ignites the mixture to form hot combustion gases. The hot combustion gases are directed into a turbine, where the expansion of the hot combustion gases drives the stages of a turbine, which, in turn drives the compressor, as the compressor is coupled to the turbine via a shaft. The exhaust gases exiting the turbine can then be used as a source of propulsion, as typical in an aircraft engine, or in powerplant operations to turn a shaft coupled to a generator for producing electricity. 
         [0004]    The exact type and size of combustion systems used in a gas turbine engine can vary depending on a variety of factors such as engine geometry, performance requirements, and fuel type. For example, the combustion system of a gas turbine engine can comprise a plurality of individual combustors. Each combustor can typically include at least one fuel injection means and ignition source, and may in fact have multiple fuel injection sources. 
         [0005]    The combustor can comprise one or more individual combustion systems. The combustor receives the air from the compressor, mixes fuel within the compressed air, and exposes this mixture to a flame source, causing the fuel-air mixture to ignite. Through the combustion process, the fuel-air mixture rapidly increases in temperature and provides the heated air to a turbine for driving the turbine. 
         [0006]    One of the components of a gas turbine combustor is an end cover. The end cover, such as the prior art end cover  10  of  FIG. 1 , encloses a combustion system. Combustion systems an often employ a plurality of fuel nozzles, with the fuel nozzles often utilizing both fuel and air injection capabilities. The end cover is used to direct fuel(s) and air to the fuel nozzles from supply lines. In fact, many gas turbine combustors operate on multiple fuel types, such as a gaseous fuel and a liquid fuel. Therefore, for an end cover of a gas turbine combustor operating on both liquid and gaseous fuel, it is conceivable that the end cover will have a very complex design to keep fuels and air sources separate, yet both supplied to the plurality of fuel nozzles. 
         [0007]    In order to keep the various fuel and air sources separate, end covers  10  of the prior art often involve a series of cavities and brazed inserts to form internal passageways within the end cover. Referring to  FIG. 1 , the end cover  10  comprises a series of fuel and air passageways within the cover. The passageways are at least in part formed by a brazed insert  12  which is configured in a way, such that when it is joined to the end cover  10 , a series of distinct passageways are formed. A brazed insert  12  allows for more rudimentary machining of the cover  10 . However, joints around the brazed inserts  12  have been known to crack or fail. 
       SUMMARY 
       [0008]    In accordance with the present invention, there is provided a novel and improved system and method for distributing fuel and air within a cover of a gas turbine combustor. More specifically, an embodiment of the present invention comprises a cover for a gas turbine combustor having a forward face and an opposing aft face spaced a distance apart thereby establishing a cover thickness. The cover also has a central passageway extending through the cover along a central axis for supplying a gaseous fuel to a first fuel nozzle positioned along the central axis. The cover also includes a plurality of fuel and air circuits positioned within the cover, where the fuel and air circuits are split between a first portion and second portion. Each of the fuel and air circuits in the first portion comprises a first core passage extending along a first circuit centerline, a cooling air supply annulus positioned radially outward of the first core passage, an atomizing air supply annulus positioned such that it intersects the core passage, and a first gas fuel supply annulus located adjacent the aft face of the cover. Each of the fuel and air circuits in the second portion comprises a second core passage extending along a second circuit centerline, a cooling air supply annulus positioned radially outward of the second core passage, an atomizing air supply annulus positioned such that it intersects the core passage, and a second gas fuel supply annulus positioned adjacent a radially outer edge of the cover, proximate the forward face. 
         [0009]    In an alternate embodiment of the present invention, a cover for a gas turbine is provided comprising a generally cylindrical disk having a forward face, an opposing aft face thereby establishing a thickness therebetween. The cover has a central passageway extending through the cover along a central axis, a first portion of fuel and air circuits positioned within the end cover and arranged in an annular array about the cover, and a second portion of fuel and air circuits positioned within the end cover and arranged in an annular array about the cover. The first portion comprises a first core passage extending along a first circuit centerline, a cooling air supply annulus positioned radially outward of the first core passage, and a first gas fuel supply annulus positioned adjacent the aft face of the cover, where the first cooling air supply annulus and first gas fuel supply annulus provide gas fuel and air to a first plurality of fuel nozzles coupled to the forward face of the cover through angled feed holes. The second portion of fuel and air circuits are also positioned within the end cover and arranged in an annular array about the cover, the second portion comprising a second core passage extending along a second circuit centerline, a cooling air supply annulus positioned radially outward of the second core passage, and a second gas fuel supply annulus positioned adjacent a radially outer edge of the cover and the forward face of the cover, where the cooling air supply annulus provides air to a second plurality of fuel nozzles coupled to the forward face of the cover through angled feed holes. 
         [0010]    In yet another alternate embodiment of the present invention, a generally cylindrical disk having a forward face, an opposing aft face thereby establishing a thickness therebetween, a central passageway extending through the thickness of the cover along a central axis, a center fuel nozzle coupled to the disk and in fluid communication with the central passageway, an annular array of fuel and air circuits, the fuel and air circuits split into a first portion and a second portion, a first plurality of fuel nozzles coupled to the fuel and air circuits of the first portion, and a second plurality of fuel nozzles coupled to the fuel and air circuits of the second portion. 
         [0011]    In an alternate embodiment of the present invention there is provided a method of fabricating a combustor end cover comprising providing a disk of material, machining a pattern of bolt holes into the disk and machining a central passageway through the disk, a first gas fuel supply annulus in an aft face of the disk, atomizing air and diffusion air annuli in the aft face of the disk, and a second gas fuel supply annulus in a forward face of the disk. A first fuel plenum and second fuel plenum are machined into the forward face of the disk. A plurality of feed holes are drilled at an angle between the first gas fuel supply annulus and the first fuel plenum as well as between the cooling air supply annuli and the air plenums. Once all of the angled feed holes have been drilled, covers are welded over the various annuli on the aft face and forward face of the disk. The cavities for the fuel nozzles are final machined and the nozzle inserts for the fuel nozzles are then welded into place. Finally, the forward and aft faces are final machined and the fuel inlet piping is welded to the aft face of the disk. 
         [0012]    In yet another alternate embodiment of the present invention, a distribution system for delivering fuel and air to a fuel nozzle is provided comprising an end cover having an aft face and a forward face with a center passageway extending through a thickness of the cover along a central axis. The first core passage extending along a first circuit centerline, a cooling air supply annulus positioned radially outward of the first core passage, an atomizing air supply annulus positioned such that it intersects the core passage, and a first gas fuel supply annulus located adjacent the aft face of the cover. Each of the fuel and air circuits in the second portion comprises a second core passage extending along a second circuit centerline, a cooling air supply annulus positioned radially outward of the second core passage, an atomizing air supply annulus positioned such that it intersects the core passage, and a second gas fuel supply annulus positioned adjacent a radially outer edge of the cover, proximate the forward face. The cooling air supply annulus, first gas fuel supply and second gas fuel supply are each in fluid communication with a corresponding distribution annulus via a plurality of feed holes. The fuel distribution annulus and air distribution annulus are formed in the cover by removing material of the cover proximate the forward and aft faces such that the fuel and air passageways formed within the cover are formed through all material of the cover. 
         [0013]    Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0015]      FIG. 1A  is a perspective view of a gas turbine combustor cover in accordance with the prior art; 
           [0016]      FIG. 1B  is a perspective view of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0017]      FIG. 2A  is a cross section view of a gas turbine combustor cover in accordance with the prior art; 
           [0018]      FIG. 2B  is a cross section view of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0019]      FIG. 3A  is a cross section view of a center gas fuel portion of a gas turbine combustor cover in accordance with the prior art; 
           [0020]      FIG. 3B  is a cross section view of a center gas fuel portion of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0021]      FIG. 4A  is a cross section view of a diffusion air passage portion of a gas turbine combustor cover in accordance with the prior art; 
           [0022]      FIG. 4B  is a cross section view of a diffusion air passage portion of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0023]      FIG. 5A  is an alternate cross section view of a gas turbine combustor cover in accordance with the prior art; 
           [0024]      FIG. 5B  is an alternate cross section view of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0025]      FIG. 6A  is a partial cross section view of a fuel passageway of a gas turbine combustor cover in accordance with the prior art; 
           [0026]      FIG. 6B  is a partial cross section view of a fuel passageway of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0027]      FIG. 7A  is a partial cross section view of an alternate fuel passageway of a gas turbine combustor cover in accordance with the prior art; 
           [0028]      FIG. 7B  is a partial cross section view of an alternate fuel passageway of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0029]      FIG. 8A  is an alternate cross section view of a gas turbine combustor cover in accordance with the prior art; 
           [0030]      FIG. 8B  is an alternate cross section view of a gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0031]      FIG. 9A  is a perspective view of an aft face of the gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0032]      FIG. 9B  is a perspective view of a forward face of the gas turbine combustor cover in accordance with an embodiment of the present invention; 
           [0033]      FIG. 10A  is a perspective view of an aft face of the gas turbine combustor cover during the machining process in accordance with an embodiment of the present invention; 
           [0034]      FIG. 10B  is a perspective view of a forward face of the gas turbine combustor cover during the machining process in accordance with an embodiment of the present invention; 
           [0035]      FIG. 11A  is a perspective view of an aft face of the gas turbine combustor cover during a step of the manufacturing process in accordance with an embodiment of the present invention; 
           [0036]      FIG. 11B  is a perspective view of a forward face of the gas turbine combustor cover during a step of the manufacturing process in accordance with an embodiment of the present invention; 
           [0037]      FIGS. 12A and 12B  are cross section views taken through the gas turbine combustor cover at various orientations to depict the internal fuel and air circuits of the cover in accordance with an embodiment of the present invention; 
           [0038]      FIG. 13A  is a perspective view of an aft face of the gas turbine combustor cover depicting the fuel and air feed holes in the cover in accordance with an embodiment of the present invention; 
           [0039]      FIG. 13B  is a perspective view of a forward face of the gas turbine combustor cover depicting the fuel and air feed holes in the cover in accordance with an embodiment of the present invention; 
           [0040]      FIGS. 14A and 14B  are cross section views taken through the gas turbine combustor cover at various orientations to show the fuel and air feed holes of the cover in accordance with an embodiment of the present invention; 
           [0041]      FIG. 15A  is a perspective view of an aft face of the gas turbine combustor cover depicting the enclosed fuel and air annuli in the cover in accordance with an embodiment of the present invention; 
           [0042]      FIG. 15B  is a perspective view of a forward face of the gas turbine combustor cover depicting the enclosed fuel and air annuli in the cover in accordance with an embodiment of the present invention; 
           [0043]      FIGS. 16A and 16B  are cross section views taken through the gas turbine combustor cover of  FIGS. 15A and 15B , respectively, at various orientations to depict the internal fuel and air circuits of the cover in accordance with an embodiment of the present invention; 
           [0044]      FIG. 17A  is a perspective view of an aft face of the gas turbine combustor cover depicting the final machined fuel and air cavities in the cover in accordance with an embodiment of the present invention; 
           [0045]      FIG. 17B  is a perspective view of a forward face of the gas turbine combustor cover depicting the final machined fuel and air cavities in the cover in accordance with an embodiment of the present invention; 
           [0046]      FIG. 18A  is a perspective view of an aft face of the gas turbine combustor cover depicting nozzle inserts welded in place in the cover in accordance with an embodiment of the present invention; 
           [0047]      FIG. 18B  is a perspective view of a forward face of the gas turbine combustor cover depicting nozzle inserts welded in place in the cover in accordance with an embodiment of the present invention; 
           [0048]      FIG. 19A  is a perspective view of an aft face of the gas turbine combustor cover depicting the fuel and air manifold piping welded in place in the cover in accordance with an embodiment of the present invention; 
           [0049]      FIG. 19B  is a perspective view of a forward face of the gas turbine combustor cover depicting the fuel and air manifold piping welded in place in the cover in accordance with an embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. 
         [0051]    The present invention is described in detail in relation to  FIGS. 1B-8B  and  9 A- 19 B. The present invention relates to an improved cover design for a gas turbine combustor where the cover geometry eliminates the need for brazing joints within the cover while providing improved channel design for directing fuel and air through the cover. As discussed above, the prior art combustor covers typically required a series of braze joints to be able to facilitate the complex flow of fuels and air within the cover to the various fuel nozzles. Due to various thermal and mechanical conditions, the braze joints have been known to crack and allow fuel to leak into non-fuel passages of the cover, causing additional fuel to be injected into the combustion process and resulting in higher operating emissions and expensive repairs to the cover. 
         [0052]    The present invention relates to a cover that is capable of being used in conjunction with a Dry Low NOx (DLN) 2.6 Combustion System or similar hardware, where the combustor has a fuel nozzle along the central axis A-A (see  FIG. 2B ) and a series of five other fuel nozzles arranged in an annular array about the combustor. The exact quantity and spacing of the fuel nozzles in the annular array may vary depending on the combustor geometry. The cover  100  provides the capability of directing a gaseous fuel and/or a liquid fuel to be passed to the series of fuel nozzles. 
         [0053]    Referring initially to  FIGS. 1A and 1B , a side-by-side comparison of the cover of the present invention  100  ( FIG. 1B ) is shown compared to the cover  10  of the prior art ( FIG. 1A ). From the external view point, there are few noticeable differences. Accordingly, maintaining the external geometry of the prior art cover permits complete interchangeability with respect to the fuel and air feed sources (not shown) and the fuel nozzles (not shown) to be coupled to the cover. 
         [0054]    Referring now to  FIGS. 2A and 2B , improvements in the cover  100  can be seen when the cover  100  is viewed in cross section. The cover  100 , which is generally circular in shape comprises a forward face  102  and an opposing aft face  104 , where the aft face  104  is spaced a distance from the forward face  102 , thereby establishing a cover thickness T. Referring to  FIGS. 2B and 3B , the cover  100  also comprises a central passageway  106  which extends through the cover  100  along a central axis A-A. The central passageway  106  is used to supply a gaseous fuel to a first fuel nozzle (not shown) that is also located along the central axis A-A and secured to the forward face  102  of the cover  100  adjacent machined features  108 . The machined features  108  of cover  100  replaces brazing in a machined component  14  into cover  10  via a braze joint  16 , as shown in  FIG. 3A . 
         [0055]    The cover  100  further comprises a plurality of fuel and air circuits, as shown by FIGS.  2 B and  4 B- 7 B. As discussed above, one such use of the cover  100  is with a DLN 2.6 combustor, produced by General Electric Company. The DLN 2.6 combustor relies on a sequencing or staging of three main fuel nozzle circuits known more commonly as PM 1 , PM 2 , and PM 3 , coupled to the cover of the combustor. The combustor operates in modes which are made of different fuel circuit combinations—known more commonly as M 1  through M 6 . The PM 1  circuit fuels the nozzle positioned along the central axis A-A. The PM 2  circuit fuels two of the five outer nozzles, which are arranged in an annular array about the central axis A-A, while the PM 3  circuit fuels the remaining three outer nozzles. The three circuits, PM 1 , PM 2 , and PM 3  work to stage fuel to the six fuel nozzles attached to the cover. 
         [0056]    Referring now to  FIGS. 11B and 13B , the plurality of fuel and air circuits are divided into a first portion  110  and a second portion  112 . For an embodiment of the present invention, the first portion  110  of the fuel and air circuits comprise the PM 2  system discussed above, and supplies fuel and air to two fuel nozzles located in the annular array about central axis A-A. More specifically, referring to  FIGS. 4B and 6B , the first portion  110 , which is located radially outward of the central passageway  106 , comprises a first core passage  114  extending along a first circuit centerline B-B. A cooling air supply annulus  116  is positioned about the first core passage  114  and is in fluid communication with an annular cooling air plenum  118  via a plurality of angled cooling air feed holes  120 . A cover  116 A is placed over annulus  116  in order to seal the annulus  116 . Also depicted in  FIG. 6B  is a first gas fuel supply annulus  122  that is in fluid communication with a first annular gas fuel plenum  124  via a plurality of angled gas feed holes  126 . The first gas fuel supply annulus  122  is positioned generally adjacent the aft face  104  of the cover  100 . A cover  122 A is placed over annulus  122  to seal the annulus  122 . The first gas fuel supply annulus  122 , which is located radially inward of the air supply annulus  116 , directs a supply of gaseous fuel into a plurality of nozzles in the PM 2  circuit. Referring back to  FIGS. 5A and 6A , prior art cover  10  utilized a feed pipe  18  which then split fuel into two feed passages  20  to the two fuel nozzles of the PM 2  circuit. Supplying fuel into an annulus, such as  122  of cover  100  in  FIG. 6B  provides a more uniform fuel distribution to the gas feed holes  126  compared to the prior art of  FIGS. 5A and 6A . In alternate embodiments of the present invention, the first core passage  114  can also provide a region through which other fluids, such as air and/or liquid fuel can flow through additional tubing. 
         [0057]    The remaining fuel and air circuits positioned in an annular array about the cover  100  form the second portion  112  and operate in the PM 3  circuit, as discussed above. These fuel and air circuits are shown in cross section in  FIG. 7B  and planar view in  FIG. 8B . More specifically, a second portion  112  of the fuel and air circuits each comprise a second core passageway  130  that extends along a second circuit centerline C-C. Similar to the first portion  110 , the second portion  112  also comprises an air circuit connected to the air supply annulus  116 , which also provides air to the first portion  110 , or PM 2  circuit. That is, air supply annulus  116  supplies air to cooling air feed holes  120  and to cooling air plenum  118 , as shown in  FIG. 7B . The air supply annulus  116  of  FIG. 7B  has a cover  116 A positioned over the annulus  116  to seal the annulus  116 . Also depicted in  FIGS. 7B and 8B  is a second gas fuel supply annulus  138  that is in fluid communication with a second annular gas fuel plenum  140  via a plurality of generally radially oriented gas feed holes  142  (see  FIG. 8B ). The second gas fuel supply annulus  138  is positioned generally adjacent the forward face  102  and a radially outer edge  144  of the cover  100  and has a cover  138 A placed over the annulus for sealing the annulus  138 . The second gas fuel supply annulus  138  directs a supply of gaseous fuel into a plurality of nozzles in the PM 3  circuit, as discussed above. In alternate embodiments, the second core passage  130  can also provide a region through which other fluids, such as air and/or liquid fuel can flow through additional tubing. 
         [0058]    Accordingly, as discussed above, and will be better understood in view of the additional discussion below, the fuel and air passageways in the cover  100  are machined in a way such that the cover  100  is fabricated from a single disk, such as that shown in  FIGS. 9A and 9B . The configurations of the fuel and air passageways contained in the cover  100  are located and oriented such that there is no longer a need for the braze joints of the prior art cover  10 , which in turn, improves the structural integrity of the cover  100 . 
         [0059]    The present invention also pertains to a method of fabricating the combustor cover  100 . The general steps and/or sequences for fabricating the cover  100  are depicted in  FIGS. 9A-19B . More specifically, referring initially to  FIGS. 9A and 9B , a disk of material, preferably a stainless steel, is provided. Next, a plurality of holes  200  are drilled into the disk as shown in  FIGS. 10A and 10B . The holes  200  extend from the aft face  104  towards the forward face  102  and are typically through holes (i.e. not threaded) and are used for securing the cover  100  to a combustor case (not shown). Located about a radially outer surface  146  are threaded holes  202 . The holes  202  are typically used to aid in lifting and moving the cover  100 . 
         [0060]    Referring now to  FIGS. 11A and 11B , a series of drilling and turning operations are performed to both the forward face  102  and aft face  104  in order to machine the various annular and axially oriented passageways. Specifically, the central passageway  106 , the cooling air supply annulus  116 , the atomizing air supply annulus  132 , the first core passage  114 , the second core passageway  130 , the first gas fuel supply annulus  122 , the second gas fuel supply annulus  138 , the cooling air plenum  118 , the atomizing air plenum  134 , the first annular gas fuel plenum  124 , and the second annular gas fuel plenum  140  are each formed through a series of turning (milling) and drilling processes. The various annular passages and axially extending passageways are depicted in  FIGS. 12A and 12B . 
         [0061]    Once the annular plenums and passageways have been machined into the forward face  102  and aft face  104  of the cover  100 , the angled feed holes  120  and  126  are drilled in the cover  100 . The angled feed holes drilled during this manufacturing step includes feed holes for the air passage  120  which connects the first cooling air supply annulus  116  to the cooling air plenum  118 . Other angled feed holes drilled at this time include the plurality of angled gas feed holes  126  for the PM 2  fuel passage. More specifically, angled gas feed holes  126  connect the first gas fuel supply annulus  122  to the first annular gas fuel plenum  124 . As it can be seen from  FIGS. 6B and 7B , the angled feed holes  120  and  126  are drilled from the aft face  104  of the cover  100  towards the front face  102 . By doing so, the angled feed holes are drilled perpendicular to the angled surface within their respective supply annulus (fuel or air), which provides a clean surface for drilling the feed holes. Feed holes  142  for the gas fuel of the PM 3  circuit are drilled radially from the second gas fuel supply annulus  138  to the second annular gas fuel plenum  140 . 
         [0062]    Once the series of annular and angled passageways are machined or drilled in the cover  100 , the various annuli are enclosed with a series of covers, as shown in  FIGS. 15A ,  15 B,  16 A and  16 B. For example, a cover  116 A encloses the cooling air supply annulus  116 , a cover  122 A encloses the first gas fuel supply annulus  122 , a cover  132 A encloses an atomizing air supply annulus  132  and a cover  138 A encloses the second gas fuel supply annulus  138 . The covers  116 A,  122 A,  132 A and  138 A are preferably fabricated from a material similar to the cover  100  and are welded to the cover  100 . 
         [0063]    Once the covers  116 A,  122 A,  132 A and  138 A have been welded in place, in-process machining to the cover occurs. More specifically, the forward face  102  and aft face  104  of the cover  100  are machined to dimension as well as the regions to which the fuel nozzles will mount and fuel supply pipes will mount, as shown in  FIGS. 17A and 17B . More specifically, as shown in  FIGS. 18A and 18B , a plurality of inserts  140 ,  141 , and  142  are positioned over the various cavities at the forward face  104  and aft face  102  of the cover  100 . The nozzle inserts  140  are welded to the cover  100  in the various annuli in order to encapsulate and meter the fuel flowing to their respective fuel nozzles. Each of the nozzle inserts  140  includes a plurality of openings which entrap removable orifices for metering the fuel flow to the fuel nozzles (not shown). 
         [0064]    Once the inserts  140 ,  141 , and  142  are in place, finish-machining of the forward face  102  and aft face  104  is completed. Once finish-machining is complete, the various fuel supply pipes  150  are secured to the forward face  104  of the cover  100 . The fuel supply pipes  150  are welded to the cover  100  and are each coupled to respective fuel supply lines. Upon completion of the cover  100 , including any welding (pipes  150 , nozzle inserts  140 , etc.), the cover may be placed in a furnace to stress relieve the cover, according to a predetermined stress relieving cycle. 
         [0065]    The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments and required operations will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. 
         [0066]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.