JP2008157615A - Replacement panel for combustor liner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of conventional replacement panels for combustor liners wherein heat stress may be induced in the panels during the operation, and if the operation is performed continuously while being subject to the heat stress, the panel causes thermal fatigue, weak points and/or cracks occur inside, and the panel must be replaced by replacing it with high cost effectiveness and high reliability since the replacement requires long time and high cost. <P>SOLUTION: This replacement panel 240 for repairing the liner of the combustor of a gas turbine engine having a combustion zone formed by an inner liner and an outer liner comprises a sheet formed of a material suitable for use in the combustion liner, at least one opening 96 formed in the sheet, a thermal barrier material 10 applied onto the sheet adjacent to at least one opening 96, and a peripheral edge part 245 not coated with the thermal barrier material 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates generally to gas turbine engines, and more particularly to combustor liner replacement panels.

  The gas turbine engine includes a compressor that compresses air. The compressed air is mixed with fuel and conveyed to the combustor. Inside the combustion chamber of the combustor, the mixture is ignited to produce hot combustion gases. At least some known combustors include a dome structure, a cowling and a plurality of liners for conveying combustion gases to the turbine. The turbine extracts energy from the combustion gas to power the compressor, as well as to generate work useful to propel the aircraft in flight or power a load such as a generator. To do. The liner is coupled to the dome structure by a cowling and extends downstream from the cowling to define a combustion chamber.

  At least some known liners include a plurality of panels joined together by riveting, bolting or welding connections. A portion of the panel includes a cooling nugget formed between adjacent panels. The nugget extends away from the combustion chamber radially outward from the panel. Accordingly, such a cooling nugget is not exposed to as much heat as the portion of the panel adjacent to the combustion chamber, and thus thermal stress may be induced inside the panel during operation. Over time, if the operation continues while receiving thermal stress, the panel will experience thermal fatigue, resulting in weakening and / or cracking inside the panel.

  Current repair methods include welding thermal fatigue cracks. Furthermore, a patch may be attached to the area of the panel weakened by thermal stress. However, if thermal stress causes thermal fatigue or thermal breakdown across a large area of the panel or across multiple panels, the combustor cannot maintain sufficient structural integrity to allow patching within such panels. There is a case. The use of welds and patches is further complicated by the fact that openings such as cooling holes or dilution holes are located in the panel and a thermal barrier coating is used. In such a case, panel repair is not feasible and the entire combustor liner is replaced.

  Because the liner is coupled to the cowl and dome structure, the entire combustor often must be dismantled when replacing the liner. In addition, when fasteners are removed from the cowl and dome structure, the precise dimensional relationship between the components can be distorted, resulting in the need for special tools for reassembly. Therefore, replacement of the combustor liner including the cooling nugget is a time consuming and costly process.

  A replacement panel for repairing a gas turbine engine combustor liner having a combustion zone formed by an inner liner and an outer liner includes a sheet of material suitable for use with the combustor liner, and a sheet of material. At least one opening formed, a thermal barrier material applied to a sheet of material adjacent to the at least one opening, and a peripheral edge to which no thermal barrier material is applied.

  FIG. 1 is a diagram schematically illustrating a gas turbine engine 10. The gas turbine engine 10 includes a low pressure compressor 12, a high pressure compressor 14 and a combustor 16. The engine 10 further includes a high pressure turbine 18 and a low pressure turbine 20. The low pressure compressor 12 and the low pressure turbine 20 are coupled by a first shaft 22, and the high pressure compressor 14 and the high pressure turbine 18 are coupled by a second shaft 21. In one embodiment, gas turbine engine 10 is a GE90 engine commercially available from General Electric Aircraft Engines, Cincinnati, Ohio. In another embodiment, gas turbine engine 10 is a CF engine commercially available from General Electric Aircraft Engines, Cincinnati, Ohio.

  In operation, air flows through the low pressure compressor 12 and compressed air is supplied from the low pressure compressor 12 to the high pressure compressor 14. The air compressed to a high pressure is sent to the combustor 16. The air flow from the combustor 16 drives the turbines 18 and 20 and exits the gas turbine engine 10 through the nozzles 24.

  FIG. 2 is a partial cross-sectional view showing the combustor 30. 3 and 4 are enlarged views showing each part of the combustor 30. The combustor 30 may be used in combination with the gas turbine engine 10 shown in FIG. 1 and includes a dome structure 32. A fuel injector (not shown) extends into the dome structure 32 and injects atomized fuel through the dome structure 32 and into the combustion zone 36 of the combustor 30 to form an air / fuel mixture. The air / fuel mixture is ignited downstream of the fuel injector.

  The combustion zone 36 is formed by a radially outer annular support member (not shown), a radially inner annular support member (not shown) and a combustion liner 40. The combustion liner 40 shields the outer support member and the inner support member from heat generated within the combustion zone 36. Combustion liner 40 includes an inner liner 42 and an outer liner 44. Each liner 42 and 44 is annular and includes a multi-nugget region 46 and a multi-hole region 48. Each multi-nugget region 46 extends downstream from the dome structure 32 to each multi-hole region 48.

  Liners 42 and 44 define a combustion zone 36. The combustion zone 36 extends downstream from the dome structure 32 to a turbine nozzle (not shown). The outer liner 44 and the inner liner 42 each include a plurality of panels 50. Panel 50 includes a series of steps 52, each step forming a separate part of combustion liner 40.

  The outer liner 44 includes a bolt band 60 and a first panel 64, and the inner liner 42 includes a bolt band 62 and a first panel 66. The outer bolt band 60 and the inner bolt band 62 are disposed adjacent to the dome structure 32 and extend downstream from the dome structure 32 to the corresponding first panels 64 and 66, respectively. The first panel 64 is coupled downstream from the bolt band 60, and the first panel 66 is coupled downstream from the bolt band 62. Each downstream adjacent panel 50 is numbered sequentially. That is, the second panel 68 is coupled downstream from the corresponding first panel 64, and the second panel 70 is coupled downstream from the corresponding first panel 66. Bolt bands 60 and 62 include a plurality of openings 72 sized to receive fasteners 74 therethrough. Fastener 74 secures liners 42 and 44, bolt bands 60 and 62, and cowl structure 78 to dome structure 32.

  Each combustor panel 50 includes a combustor liner surface 80, an outer surface 82 and an overhang portion 84. Combustor liner surface 80 extends from dome assembly 32 to the turbine nozzle. Combustor liner surface 80 and outer surface 82 are joined together at an overhang portion 84 to form a rearward edge 86. A plurality of air cooling structures 88 separate adjacent combustor panels 50.

  The air cooling structure 88 includes a plurality of openings 90. The opening 90 receives air from an air plenum (not shown) so that a thin protective boundary layer of air is formed between the hot combustion gas and the combustor liner surface 80. In addition, the opening 90 allows convective cooling of the combustor liner 40. In particular, the opening 90 passes through a structure 88 formed radially inward from a nugget 92 formed by the panels 50 between adjacent panels 50. Since the panels 50 are coupled in series, the downstream end 100 of each panel is coupled to the upstream end 102 of the adjacent downstream panel 50. A nugget 92 is formed between the downstream end 100 and the upstream end 102 of the adjacent bonded panels.

  The liner multi-nugget region 46 includes a plurality of nuggets 92. In the present embodiment, the multi-nugget region 46 includes three nuggets 92. The liner multi-hole region 48 includes a plurality of openings 96 (representative openings 96 are shown). Other areas of the liner may include a multi-hole opening 96 as shown in FIGS.

  A layer 110 of thermal barrier material is applied to the combustor liner surface 80. The thermal barrier material further isolates the combustor liner surface 80 from the hot combustion gases. In one embodiment, the thermal barrier coating material is commercially available from Englehart Industries, Wilmington, Massachusetts.

  During operation, heat is generated within the combustion zone 36 while atomized fuel is injected into the combustion zone 36 and ignited. Although air enters the combustion zone 36 through the cooling structure 88 and forms a thin protective boundary layer of air along the combustor liner surface 80, the combustor liner surface is not uniformly exposed to high temperatures, Thermal stress is generated on the panel 50. If the panel 50 is exposed to thermal stress over time, the panel 50 may deteriorate.

  The degraded area of the combustor liner 40 may be removed and replaced using the methods described herein. In particular, the degraded areas of each liner multi-nugget area 46 and / or each liner multi-hole area 48 may be removed and replaced using the methods described herein.

  In a field return engine, such as engine 10, if the combustor liner multinugget region 46 is shown to include at least one degraded panel 50, the combustor liner 40 may be penetrated to remove the degraded panel 50. As a result, a peripheral cut is formed. In particular, as shown by line 120, a notch extends from liner outer surface 82 to liner inner surface 80 as shown by line 120, and a portion 122 of panel body 104 of panel 50 to be cut is secured to the interior of combustor 30. The cuts are formed in the radial direction through the liner 40 and through the panel body 104 so that they remain intact. Further, the cuts are formed through the liner 40 downstream from the degraded panel 50 to be replaced. Upon removal, the fastener 74 may be loosened to separate the degraded panel 50 from the liner 40. Alternatively, in order to form an opening or a missing portion (defect) in the liner, the deteriorated panel 50 can be separated from the combustor liner 40 and removed from the combustor liner 40 to the upstream side. Two cuts may be formed.

  By repairing the combustor liner as described above, the fully annular segment of the liner may be replaced with a suitable equivalent annular liner segment. Accordingly, a replacement panel for this type of combustor liner repair has the size, shape and structure shown for the original liner in the accompanying drawings. Alternatively, the repair may be performed using a partial annular segment that is shaped to correspond to the removed segment of the combustor liner, such as the replacement panel 240 shown in FIGS. Repairs may also be performed using separate patches with multiple replacement panels.

  After the degraded panel 50 is removed from the combustor liner 40, replacement panels may be installed on the combustor liners 42 and / or 44. If desired, the replacement panel is formed to include a nugget configuration that is substantially the same as the portion of liner 40 to be replaced. In one embodiment, at least one of a forging, forging ring or casting is used as the replacement panel.

  The replacement panel may be formed from a flat material sheet or a substantially flat material sheet. Thereafter, the material sheet is formed into the required shape to accommodate the loss of the liner to be replaced. This shaping may include shaping a sheet of material into a cylindrical, semi-cylindrical, spherical, hemispherical or any shape as required. If necessary, openings are formed in the material to meet the conditions of the missing or removed portion of the combustor liner. These openings may include holes of various patterns and sizes. When viewed in plan view, the panel may be square, rectangular or any other shape suitable for use in replacing an applicable defect in the combustor liner.

  The replacement panel is then welded to the combustor liner 42 and / or 44 to be welded to an existing panel 50 that remains secured within the combustor liner 42 and / or 44. In particular, the downstream side (not shown) of the body of the replacement panel is welded to the panel body portion 122 inside the combustor 30. In one embodiment, electron beam (EB) welding is used to secure the replacement panel inside the combustor 30. In another embodiment, tungsten inert gas (TIG) welding is used to secure the replacement panel inside the combustor 30. Next, a thermal barrier coating film material may be applied to the peripheral edge of the replacement panel and the combustor liner surface 80 in the vicinity of the weld or other securement and after inspection of the quality of the opening 96. In order to maintain this state, a protective mask may be disposed so as to cover the opening 96. Thereafter, the fastener 74 is tightened again.

  In a field return engine, such as engine 10, if the combustor liner multi-hole region 48 is shown to include at least one degraded panel 50, the combustor liner 40 may be penetrated to remove the degraded panel 50. A notch is formed. In particular, as shown by line 120, the incision extends from liner outer surface 82 to liner surface 80 and panel body portion 122 remains secured within combustor 30 as shown in FIG. In addition, the peripheral cut is formed in the radial direction from the liner 40 through the panel body 104. In addition, the cut is formed through the liner 40 downstream from the degraded panel 50 to be replaced. Thereafter, the deteriorated portion of the multi-hole region 48 is separated from the combustor liner 40 and becomes removable, and as a result, an opening or a missing portion (defect) is formed in the liner. In addition, a second cut may be formed upstream from the deteriorated panel 50 to be replaced. Next, if necessary, the fasteners 74 may be loosened to separate them from the liner 40 to remove the degraded portions and the multi-nugget region 46.

  By performing combustor liner repair as described above, the complete annular segment of the liner may be replaced with a comparable or compatible annular liner segment. Accordingly, a replacement panel for this type of combustor liner repair has the size, shape and structure shown for the original liner in the accompanying drawings. Alternatively, the repair may be performed by a partial annular segment, such as a replacement panel 240 shown in FIGS. 6 and 7, with a plurality of shapes formed to correspond to the removed segments of the combustor liner. The repair may be performed using a separate patch formed by the replacement panel.

  After the deteriorated portion of the multi-hole region 48 is removed from the combustor 30, a replacement panel may be installed in the combustor 30. In one embodiment, at least one of a forging, forging ring, casting or sheet metal panel is manufactured and used as a replacement panel. Before the replacement panel is mounted, the multi-hole region 96 is formed in the replacement panel in advance. If necessary, a thermal barrier coating film 110 is further applied including the vicinity of the opening 96 so as to cover the edge of the opening 96 and the surrounding surface of the replacement panel. In one embodiment, the opening is formed by laser processing. In another embodiment, the opening is formed using an electro-discharge machining (EDM) process. In yet another embodiment, the newly formed opening may be sized differently and reduced or placed at a different location to improve the cooling of the combustor 30. Also good.

  The replacement panel may be formed from a flat material sheet or a substantially flat material sheet. Thereafter, the material sheet is formed into the required shape to accommodate the loss of the liner to be replaced. This shaping may include shaping a sheet of material into a cylindrical, semi-cylindrical, spherical, hemispherical or any shape as required. If necessary, openings are formed in the material to meet the conditions of the missing or removed portion of the combustor liner. These openings may include holes of various patterns and sizes. When viewed in plan view, the panel may be square, rectangular or any other shape suitable for use in replacing applicable defects in the combustor liner.

  The replacement panel may be sized and shaped to fit the particular part being removed from the liner 140, or may be pre-manufactured in one or more commonly used sizes and shapes. The replacement panel may include one or more openings 96 through the panel and a thermal barrier material 110 applied to at least one surface. The thermal barrier material 110 may be applied on both sides and may be applied to cover the edges of one or more openings 96. However, the thermal barrier material 110 is not applied to at least a portion of the peripheral edge 250 of the replacement panel (see replacement panel 240 shown in FIGS. 6 and 7) to facilitate anchoring to the liner 140. . The thermal barrier material 110 may not be applied to substantially all or the entire peripheral edge 250. The replacement panel 240 may further include a chamfered edge 245 to facilitate performing a welding process or other securing process.

  Prior to installation, the opening 96 is formed in the multi-hole region of the replacement panel and the thermal barrier material 110 is applied to inspect and verify the air flow characteristics of the opening 96 under controlled factory conditions. Can be used for quality inspection of replacement panels. In order to facilitate the fixation of the replacement panel, the thermal barrier material remains substantially unapplied to the peripheral portion of the replacement panel.

  The replacement panel is then welded to the existing panel 50 that remains secured inside the combustor 30. In particular, the downstream side (not shown) of the replacement panel body is welded to the panel body portion 122 inside the combustor 30. In one embodiment, electron beam (EB) welding is used to secure the replacement panel inside the combustor 30. In another embodiment, tungsten inert gas (TIG) welding is used to secure the replacement panel inside the combustor 30. Thereafter, a thermal barrier coating material may be applied to the peripheral edge of the replacement panel 240 and the combustor liner surface 80 in the vicinity of the weld or other securement, and the quality of the opening 96 is inspected. In order to maintain a later state, a protective mask may be disposed so as to cover the opening 96.

  Because the degraded liner is replaced using the method described herein, an improved replacement process is used in terms of savings compared to removing and replacing the entire combustor liner 40. Thus, the combustor 30 is returned to the use state. Furthermore, since the replacement panel is formed to be substantially the same as the panel 50 originally installed, the replacement panel does not adversely affect the aerodynamic performance and the combustor performance.

  FIG. 4 is an enlarged cross-sectional view illustrating another embodiment of an inner combustor liner 140 that may be used with gas turbine engine 10 (shown in FIG. 1). FIG. 5 is an enlarged plan view of the combustor liner 140. The liner 140 is substantially similar to the liner 40 (shown in FIGS. 2 and 3) and is installed inside a combustor (not shown). The combustor includes a combustor liner that includes an annular inner liner 140 and an annular outer liner (not shown) formed substantially similar to the inner liner 140. Inner liner 140 includes a plurality of panels 150. Panel 150 includes a series of steps 152, each step 152 forming a separate portion of combustor liner 140.

  Panels 150 are coupled in series. The inner liner 140 includes a bolt band 160 and a first panel 164. The inner bolt band 160 is coupled to a dome structure (not shown) and extends downstream from the dome structure to the first panel 164. The first panel 164 and the panel 150 are coupled downstream from the bolt band 160 so that each adjacent downstream panel 150 is sequentially numbered. Accordingly, the second panel 168 is coupled downstream from the first panel 164, and the third panel 170 is coupled downstream from the second panel 168. Bolt band 160 includes a plurality of openings 172 sized to receive fasteners 74 (shown in FIG. 2) for securing liner 140 to the dome structure.

  Each combustor panel 150 includes a combustor liner surface 180, an outer surface 182, and an overhang portion 184. Combustor liner surface 180 extends from the dome structure to the turbine nozzle. Combustor liner surface 180 and outer surface 182 are joined together at overhang portion 184 to form a rearward edge 186. A plurality of air cooling structures 188 separate adjacent combustor panels 150.

  The air cooling structure 188 includes a plurality of openings 190. The opening 190 receives air from an air plenum (not shown) so that a thin protective boundary layer of air is formed between the hot combustion gas and the combustor liner surface 180. Opening 190 is known as a dilution opening and extends between liner surface 180 and outer surface 182 to facilitate mixing of combustion gases within the combustor. In the present embodiment, the opening 190 is substantially circular. In particular, each panel 150 includes an upstream end 200, a downstream end 202, and a body 204 extending between the ends. The panels 150 are coupled such that the downstream end 202 of each panel is coupled to the upstream end 200 of the adjacent downstream panel 150. A nugget 192 is formed between the downstream end 202 and the upstream end 200 of each adjacent joined panel. Nugget 192 is known as a super slot nugget. In this embodiment, the liner 140 includes six nuggets 192. As shown in FIGS. 4 and 5, each region of the liner may include a multi-hole opening 96.

  In another embodiment, a layer of thermal barrier material (not shown) is applied to the combustor liner surface 180. The layer of thermal barrier material improves the ability to thermally protect the combustor liner surface 180 from hot combustion gases.

  The degraded area of the combustor liner 140 may be removed and replaced using the methods described herein. In a field return engine, such as engine 10, if the combustor liner 140 is shown to include at least one degraded panel 150, the combustor liner 140 passes through the surroundings to remove the degraded panel 150. A cut is formed in the direction. In particular, as shown in FIG. 4, the circumferential incision is formed radially through the liner 140 and nugget 192 so that the incision extends from the liner outer surface 182 to the liner surface 180 as indicated by line 220. Is done. In one embodiment, the notch is formed between the third panel 170 and the fourth panel 222. Further, the cut extends through the liner 140 and downstream from the deteriorated panel 150 to be replaced.

  By performing repairs to the combustor liner as described above, the complete annular segment of the liner may be replaced with a comparable or compatible annular liner segment. Accordingly, a replacement panel for this type of combustor liner repair has the size, shape and structure shown for the original liner in the accompanying drawings. Alternatively, the repair may be performed by a partial annular segment, or a plurality of shapes formed to correspond to the removed segment of the combustor liner, such as the replacement panel 240 shown in FIGS. The repair may be performed using a separate patch formed by the replacement panel.

  The portion removed from the combustor liner 140 may be partially or completely surrounded by the remaining portion of the combustor liner 140. Thus, the portion to be removed may form an opening in the liner, or a defect of any other size or shape in the liner.

  The replacement panel 240 may be installed on the combustor liner 140 after the degraded portion of the liner 140 is removed from the combustor. In one embodiment, at least one of a forging, forging ring, casting or sheet metal panel is manufactured and used as a replacement panel.

  The replacement panel may be formed from a flat material sheet or a substantially flat material sheet. Thereafter, the material sheet is formed into the required shape corresponding to the defect of the liner to be replaced. This forming may include forming the sheet of material into a cylindrical, semi-cylindrical, spherical, hemispherical or any required shape. If desired, openings may be formed in the material to meet the conditions of the missing or removed portion of the combustor liner, and the openings may include holes of various patterns and sizes. When viewed in plan view, the panel may be square, rectangular or any other shape suitable for use in replacing applicable defects in the combustor liner.

  The replacement panel 240 may be sized and shaped to fit a particular portion being removed from the liner 140, or may be pre-manufactured in one or more commonly used sizes and shapes. Good. The replacement panel 240 may include one or more openings 96 that penetrate the panel and a thermal barrier material 210 applied to at least one surface. The thermal barrier material 210 may be applied on both sides and may be applied to cover the edge of one or more openings 96. However, to facilitate adhesion to the liner 140, the thermal barrier material 210 is not applied to at least a portion of the peripheral edge 250 of the replacement panel 240, but the thermal barrier material is entirely applied to the peripheral edge 250. 210 may not be applied. The replacement panel 240 may further include a chamfered edge 245 to facilitate a welding process or other securing process.

  After installation, the configuration of the opening 190 is not changed, such as by applying additional thermal barrier material adjacent to the edge of one or more openings or to the edges themselves, so that the specified air flow rate prior to installation The replacement panel 240 may be inspected and tested, including “flow inspection” the opening 190 for characteristics.

  Thereafter, the replacement panel is welded to the combustor liner 140 such that the replacement panel is secured within the combustor. In particular, the downstream end (not shown) of the replacement panel is welded to the panel 150 such that a nugget 192 is formed between the replacement panel and the existing panel 150. In one embodiment, electron beam (EB) welding is used to secure the replacement panel within the combustor liner 140. In another embodiment, tungsten inert gas (TIG) welding is used to secure the replacement panel inside the combustor liner 140. A thermal barrier material may then be applied to the combustor liner surface 180 of the remaining panel.

  The combustor liner replacement method described above is cost-effective and highly reliable. The method includes removing the degraded panel from the combustor liner so that the degraded panel can be replaced with a replacement panel. In one embodiment, the degraded panel is removed by making a cut through the body of the panel, and then the replacement panel is welded to the combustor liner. As a result, a method is provided that allows costly and highly reliable removal and replacement of degraded combustor liner panels.

  While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

1 is a diagram schematically illustrating a gas turbine engine. FIG. 2 is a partial cross-sectional view showing a combustor assembly that may be used with the gas turbine engine shown in FIG. 1. FIG. 3 is an enlarged cross-sectional view showing an outer combustor liner used with the combustor shown in FIG. 2. FIG. 3 is an enlarged cross-sectional view showing another configuration of an inner combustor liner used with the combustor shown in FIG. 2. FIG. 5 is an enlarged plan view showing the combustor liner shown in FIG. 4. FIG. 5 is an enlarged partial cross-sectional view showing the combustor liner shown in FIG. 4. It is the top view which showed the panel for replacement | exchange.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gas turbine engine, 30 ... Combustor, 36 ... Combustion zone, 40 ... Combustor liner, 42 ... Inner liner, 44 ... Outer liner, 50 ... Panel, 96 ... Opening, 110 ... Thermal barrier coating film, 150 ... Panel, 240 ... Panel for replacement

Claims (7)

In a replacement panel (240) for repairing a liner (140) of a combustor (30) of a gas turbine engine having a combustion zone (36) formed by an inner liner (42) and an outer liner (44),
A sheet of material suitable for use in the combustor liner (140);
At least one opening (96) formed in the sheet of material;
A thermal barrier material (110) applied to the sheet of material adjacent to the at least one opening (96);
A replacement panel (240) having a peripheral edge (250) to which the thermal barrier material (110) is not applied.   The replacement panel (240) of claim 1, wherein the replacement panel (240) includes a plurality of openings (96).   The replacement panel (240) includes a first panel (164) and a second panel (168) joined by a nugget (192), and the second panel (168) includes a thermal barrier material (110). 2) The replacement panel (240) of claim 1, wherein the coating is not substantially applied.   The replacement panel (240) of claim 1, wherein the replacement panel (240) further comprises a chamfered edge (245).   The replacement panel (240) of claim 1, wherein the replacement panel (240) includes a plurality of openings (96) of a plurality of sizes.   The replacement panel (240) of claim 1, wherein the replacement panel (240) is formed as an annular segment.   The replacement panel (240) of claim 1, wherein the replacement panel (240) is substantially flat.

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