Patent Publication Number: US-2022235673-A1

Title: High temperature flange joint, exhaust diffuser and method for coupling two components in a gas turbine engine

Description:
BACKGROUND 
     1. Field 
     The present disclosure relates in general to the field of gas turbine engines, and in particular a high temperature flange joint connection between adjoining parts of a gas turbine engine casing. 
     2. Description of the Related Art 
     A bolted flange joint in a gas turbine engine is typically subjected to a very high steady state temperature as well as high thermal gradients. To maintain joint integrity, it may be necessary to maintain the bolt clamp load throughout transient and steady state operation. During transient operation, the flange tends to heat up and cool faster than the bolts, which results respectively in an increase or decrease of bolt preload. When the bolt preload increases, for example, during engine startup, the flange may deform plastically. Also, creep may set in at the flange due to high steady state temperatures. The plastic deformation from engine startup and steady state may reduce the overall preload of the bolt, to the extent where there is no remaining bolt preload after engine shutdown. 
     SUMMARY 
     Briefly, aspects of the present disclosure relate to a high temperature flange joint in a gas turbine engine capable of maintain bolt preload at high steady state temperatures and transient engine operation, while minimizing deformation of the flange. 
     According to a first aspect, a high temperature flange joint is provided for coupling a first component to a second component in a gas turbine engine. The flange joint comprises a first flange formed on the first component abutting a second flange formed on the second component. The flange joint further comprises a plurality of adjacently arranged bolt connections. Each bolt connection is formed through a pair of mutually aligned bolt holes in the first and second flanges. Each bolt connection comprises a first spacer plate bearing against the first flange and a second spacer plate bearing against the second flange. Each bolt connection further comprises a first lock washer and a second lock washer bearing against the first spacer plate and the second spacer plate respectively. Each bolt connection further comprises a bolt inserted through the first and second flanges, the first and second spacer plates and the first and second lock washers, the bolt being preloaded to clamp the first flange to the second flange. Each of the spacer plates has a respective thickness and being sized to enhance a bearing surface in contact with the respective flange, whereby a bolt preload is maintained during operation of the gas turbine engine. 
     According to a second aspect, a method is provided for coupling a first component to a second component in a gas turbine engine. The method comprises forming a plurality of adjacently arranged bolt connections. Each bolt connection is formed through a pair of mutually aligned bolt holes respectively in a first flange of the first component and a second flange of the second component. Forming each bolt connection comprises disposing a first spacer plate bearing against the first flange and a second spacer plate bearing against the second flange. Forming each bolt connection further comprises disposing a first lock washer and a second lock washer bearing against the first spacer plate and the second spacer plate respectively. Forming each bolt connection further comprises inserting a bolt through the first and second flanges, the first and second spacer plates and the first and second lock washers. Forming each bolt connection further comprises preloading the bolt to clamp the first flange to the second flange. Each of the spacer plates has a respective thickness and is sized to enhance a bearing surface in contact with the respective flange, whereby a bolt preload is maintained during operation of the gas turbine engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention. 
         FIG. 1  is a schematic view of a gas turbine engine; 
         FIG. 2  is a perspective sectional view of a portion of a turbine exhaust diffuser where aspects of the present disclosure may be incorporated; 
         FIG. 3  is a sectional view of a high temperature flange joint; 
         FIG. 4  is a perspective view of a high temperature flange joint with spacer plates with anti-rotation feature, according to one embodiment; 
         FIG. 5  depicts an end view of a high temperature flange joint having spacer plates with anti-rotation feature incorporating beveled interfaces, according to another embodiment; 
         FIG. 6  depicts an end view of a high temperature flange joint having spacer plates with anti-rotation feature incorporating interlocking interfaces, according to yet another embodiment; and 
         FIG. 7  is a perspective view of a high temperature flange joint having spacer plates incorporating ant-rotation tabs, according to a further embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the various embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     Referring to  FIG. 1 , a gas turbine engine  1  generally includes a compressor section  2 , a combustor section  4 , and a turbine section  8 . In operation, the compressor section  2  inducts ambient air  3  and compresses it. The compressed air from the compressor section  2  enters one or more combustors in the combustor section  4 . The compressed air is mixed with the fuel  5 , and the air-fuel mixture is burned in the combustors to form a hot working medium fluid  6 . The hot working medium fluid  6  is routed to the turbine section  8  where it is expanded through alternating rows of stationary turbine vanes and rotating turbine blades and used to generate power that can drive a rotor  7 . The expanded working medium fluid  9  is exhausted from the engine  1  via an exhaust diffuser  10  of the turbine section  8 , which is located downstream of a last row of turbine blades. 
     Aspects of the present disclosure may be used to form a high temperature flange joint at various locations in the gas turbine engine  1 . A particularly suitable implementation of the disclosed embodiments is in the exhaust diffuser  10 . A portion of an example exhaust diffuser  10  is shown in  FIG. 2 . In the shown embodiment, the exhaust diffuser  10  has an axis  11  and comprises an exhaust cylinder  12  located downstream of a last stage of turbine blades (not shown) and an exhaust manifold  14  coupled axially to and downstream of the exhaust cylinder  12 . Each of the exhaust cylinder  12  and the exhaust manifold  14  includes a respective annular ID wall  12   a ,  14   a,  and a respective annular OD wall  12   b,    14   b.  The ID walls  12   a,    14   a  and the OD walls  12   b,    14   b  respectively form an ID boundary and an OD boundary of an annular turbine exhaust flow path. A plurality of load bearing struts  16  are circumferentially arranged in the exhaust flow path of the exhaust cylinder  12 , extending through the ID wall  12   a  and the OD wall  12   b.  A plurality of load bearing struts  18  may also be circumferentially arranged in the exhaust flow path of the exhaust manifold  14 , extending through the ID wall  14   a  and the OD wall  14   b.    
     The exhaust cylinder  12  and the exhaust manifold  14  may be coupled by one or more annular flange joints. For example, a first annular flange joint  30   a  may be formed between the ID wall  12   a  of the exhaust cylinder  12  and the ID wall  14   a  of the exhaust manifold  14 . A second flange joint  30   b  may be formed between the OD wall  12   b  of the exhaust cylinder  12  and the OD wall  14   b  of the exhaust manifold  14 . Aspects of the present disclosure may be applied to either or both of the annular flange joints  30   a  and  30   b.  Aspects of the present disclosure may also be applied to linear flange joints, for example the joints  30   c  for tangentially coupling adjacent segments  22   a,    22   b  of a bearing axis panel  22 . Without limitation, the joints in an exhaust diffuser may be exposed to local temperatures around 700-800 degrees Celsius. 
     A flanged joint comprises a plurality of bolt connections through abutting flanges formed on the components to be coupled. In case of an annular flange joint, such as joints  30   a,    30   b  herein, the bolt connections are adjacently arranged along a circumferential direction. In case of a linear flange joint, such as joints  30   c  herein, the flanges extend lengthwise in an axial direction of the engine  1 , wherein the bolt connections are adjacently arranged in a straight line along the axial direction. 
     In view of the challenges associated with a high temperature flange joint in a gas turbine engine, as noted in the “Background” section of this specification, an approach for reducing the contact pressure under the washer face may be to use an oversized washer, having a larger outer diameter. In this application, however, an oversized washer typically requires the pitch circle diameter of the bolt to be increased to package the oversized washer accordingly. This would necessitate an increase in flange height, which may have a negative effect on flange fatigue life, since a taller flange results in a larger thermal gradient in a high temperature environment, such as in an exhaust diffuser. Another approach to address the stated problem may involve using low bolt preload values at assembly. However, this may potentially lead to field issues with bolt loosening, particularly during engine shutdown. The problem is further pronounced in advanced engines having higher ramp rates and exhaust temperatures. 
       FIG. 3  depicts a high temperature flange joint  30  for coupling a first component  32   a  to a second component  32   b  in a gas turbine engine, according to an embodiment of the present disclosure. The flange joint  30  may, for example and without limitation, be embodied as any of the flange joints  30   a,    30   b,    30   c  shown in  FIG. 2 . The first component  32   a,  may represent, for example, either of the components  12   a,    14   a,    22   a,  while the component  32   b  may correspondingly represent any of the components  12   b,    14   b,    22   b.  In this specification, the axes X, Y, and Z respectively represent a length direction, a thickness direction and a height direction of the flange joint. The length direction refers to a direction along which bolt connections are arranged. For the flange joints  30   a,    30   b,  the length direction corresponds to a circumferential direction of the gas turbine engine, while for the flange joint  30   c,  the length direction corresponds to an axial direction of the gas turbine engine. The thickness direction refers to a direction of extension of the bolts. The height direction is perpendicular to the length and thickness directions. In case of the flange joints  30   a,    30   b,    30   c,  the height direction corresponds to a radial direction of the gas turbine engine. 
     As shown in  FIG. 3 , the first component  32   a  has a respective flange  34   a  formed thereon, while the second component  32   b  has a respective flange  34   b  formed thereon. The flanges  34   a,    34   b  each have an array of bolt holes formed therethrough, respectively denoted as  38   a  and  38   b.  The array of bolt holes  38   a,    38   b  extend along the length direction of the flange joint  30 , which is perpendicular to the plane of  FIG. 3 . At the time of assembly of the components  32   a,    32   b,  the flanges  34   a,    34   b  abut such that the bolt holes  38   a,    38   b  on the respective flanges  34   a,    34   b  are mutually aligned. The flange joint  30  includes a plurality of bolt connections  40  arranged adjacently along the length direction, each bolt connection  40  being formed through a pair of mutually aligned bolt holes  38   a,    38   b  in the first and second flanges  34   a,    34   b.  Each bolt connection  40  comprises a first spacer plate  42   a  bearing against the first flange  34   a  and a second spacer plate  42   b  bearing against the second flange  34   b.  Each bolt connection further comprises a first lock washer  44   a  and a second lock washer  44   b  bearing against the first spacer plate  42   a  and the second spacer plate  42   b  respectively. A bolt  46  is inserted through the first and second flanges  34   a,    34   b,  the first and second spacer plates  42   a,    42   b  and the first and second lock washers  44   a,    44   b.  The bolt  46  is preloaded, herein by tightening a respective nut  48  by applying an appropriate torque, to clamp the first flange  34   a  to the second flange  34   b.  Each of the spacer plates  42   a,    42   b  has a respective thickness t a , t b . Each spacer plate  42   a,    42   b  is further sized to enhance a bearing surface in contact with the respective flange  34   a,    34   b.  In one embodiment, each of the spacer plates  42   a,    42   b  may be sized such that a bearing surface  56   a,    56   b  of the spacer plate  42   a,    42   b  substantially covers a bearing face  58   a ,  58   b  of the respective flange  34   a,    34   b  along a length L of the spacer plate  42   a,    42   b.    
     As per the described embodiment, the bearing area of contact with the flanges  34   a,    34   b  is significantly increased over what can be achieved by an oversized washer, without increasing the height of the flanges  34   a,    34   b.  This reduces flange thermal gradients and improves component fatigue life. Increased bearing area results in reduced contact pressure, which, in turn, reduces creep deformation of the flanges  34   a,    34   b  and loss of bolt preload. This obviates the need for high grade flange materials, such as nickel alloys, and allows low strength materials, such as austenitic stainless steel to be used in the flanges. In one embodiment, the flanges  34   a,    34   b  may thereby be formed of a material having a lower yield strength than a material of the spacer plates  42   a,    42   b.  An additional benefit is achieved by the thickness of the spacer plates  42   a,    42   b.  Since the bolt preload extends below the washers  44   a,    44   b,  through the spacer plates  42   a,    42   b  in a conical distribution, the thicker the spacer plates  42   a ,  42   b,  the larger the pressure distribution on the flanges  34   a,    34   b.  Furthermore, due to the thickness of the of the spacer plates  42   a,    42   b,  the bolt head  46   a  is located further away from the flanges  34   a,    34   b,  whereby bolt temperature is lowered. The decreased bolt temperatures allow use of lower grade bolt material. The shown configuration maintains bolt preload for a longer duration during operation of the gas turbine engine, which extends the service interval to which the bolts must be retightened. The shown configuration requires an increased bolt length, which increases the bolt length to diameter ratio without increasing flange thickness. This allows for additional bolt stretch, which reduces the preload loss due to settling without affecting the flange fatigue life. 
     In some embodiments, to reduce thermal loading, the flanges  34   a,    34   b  may have a scalloped profile along the length direction (see  FIG. 4-7 ). The scalloped profile may include first portions  52  having a first height h 1  separated by second portions  54  having a second height h 2 , the first height h 1  being greater than the second height h 2 . Herein, the bolts  46  are located at the first portions  52  of the scalloped profile having increased height. In other embodiments, the flanges  34   a,    34   b  may be provided with a flat profile, having substantially constant height along the length direction. 
     In one embodiment, the lock washers  44   a,    44   b  are configured to secure the bolts  46  in position by utilizing the bolt preload. One example of such a lock washer is a bipartite wedge lock washer. The construction of a bipartite wedge lock washer is known to one skilled in the art, for example as disclosed in the patent document EP0131556B1. The use of the above-mentioned type of lock washers is particularly enabled by the herein described embodiment that is configured to substantially maintain bolt preload during engine operation. The use of such lock washers in a high temperature flange joint would provide significant reduction in complexity and time of assembly in relation to conventionally used lock washers in such applications, such as tab or pant-leg lock washers, which are positively locked to a surface and are difficult and time-consuming to bend during assembly. 
     To prevent loss of bolt preload and maintain functionality of the lock washers  44   a,    44   b  during engine operation, a further development consists in providing an anti-rotation feature to the spacer plates  42   a,    42   b  so that they do not rotate relative to the respective flange  34   a,    34   b,  for example, in the event the bolt  46  loosens. 
     As shown in  FIG. 4 , one way to achieve an anti-rotation feature is by sizing the spacer plates  42   a,    42   b  in the length direction, to accommodate multiple adjacent bolts  46  therethrough. In the shown example, each spacer plate  42   a,    42   b  is sized to extend to two adjacent bolt holes. By extending each spacer plate  42   a,    42   b  across adjacent bolts  46 , it may be ensured that if one of the bolts  46  rotates counter-clockwise to loosen, the adjacent bolt  46  on the same spacer plate rotates clockwise to tighten, thereby preventing rotation of the spacer plate. The lengthwise size of the spacer plates  42   a,    42   b  may be constrained based on the consideration that with increasing length, thermal lag may develop between the spacer plate  42   a,    42   b  and the respective flange  34   a,    34   b  that can lead to additional loading on the bolts  46  in the length direction. 
       FIGS. 5 and 6  illustrate example embodiments which provide an anti-rotation feature while minimizing thermal lag between the spacer plates  42   a,    42   b  and the respective flange  34   a,    34   b.  In these example embodiments, each spacer plate  42  (generically referring to either of the spacer plates  42   a,    42   b ) may be sized lengthwise to accommodate a single bolt  46 . As shown in  FIGS. 5 and 6 , each spacer plate  42  extends lengthwise along the respective flange  34  (generically referring to either of the flanges  34   a,    34   b ) from a first edge  62  to a second edge  64 . The interfacing edges  62  and  64  of adjacent spacer plates may be configured to prevent rotation of the spacer plate  42  in relation the flange  34 . 
     In the embodiment of  FIG. 5 , the first edge  62  and the second edge  64  of each spacer plate  42  are beveled, i.e., inclined at an angle that is non-parallel and non-orthogonal to the length direction. The beveled edges  62 ,  64  of one spacer plate  42  are configured to interface with beveled edges  64 ,  62  of adjacent spacer plates  42  on opposite sides. The bevel is at an angle such that if one of the spacer plates  42  were to rotate counter-clockwise (for example, due to bolt loosening) as shown by the arrow  82 , then it would create a clockwise rotation (bolt tightening) on the adjacent bolts on either side, as shown by the arrow  84 . This would prevent the spacer plate  42  that is loosening from rotating further, thereby realizing an anti-rotation feature. To that end, in the shown configuration of  FIG. 5 , the first edge  62  and the second edge  64  of each spacer plate  42  may be beveled in opposite directions. 
     In the embodiment of  FIG. 6 , a similar effect is achieved by providing a gear-tooth or interlocking interface between adjacent spacer plates  42 . Herein, a first edge  62  of each spacer plate  42  defines a groove shape and the second edge  64  of the spacer plate  42  defines a tongue shape. The first edge  62  and the and second edge  64  are configured to form respective interlocking interfaces with tongue and groove shaped edges  64 ,  62  of adjacent spacer plates  42  on opposite sides. The interlocking interfaces ensure that if one of the spacer plates  42  were to rotate counter-clockwise (for example, due to bolt loosening) as shown by the arrow  82 , then it would create a clockwise rotation (bolt tightening) on the adjacent bolts on either side, as shown by the arrow  84 . 
     In a further embodiment, as shown in  FIG. 7 , an additional anti-rotation feature may be realized by providing each spacer plate  42  (generically referring to either of the spacer plates  42   a,    42   b ) with anti-rotation tabs contacting a top surface  60  of the respective flange  34  (generically referring to either of the flanges  34   a,    34   b ). In case of the illustrated flange joints  30   a,    30   b,    30   c,  the top surface is a radially outer surface of the respective flange  34   a,    34   b.  In the shown configuration, each spacer plate  42  is provided with a pair of anti-rotation tabs  72 ,  74  located respectively at a first lengthwise end  76  and a second lengthwise end  78  of the spacer plate  42 . The tabs  72 ,  74  overlap and bear against the top surface  60  of the flange  34  to prevent rotation of the spacer plate  42  relative to the flange  34 . 
     A further aspect of the present disclosure may be directed to a method for coupling a first component to a second component in a gas turbine engine, in accordance with the herein described embodiments. In one embodiment, the method may be part of servicing the gas turbine engine, including, for example, a replacement or upgrade of an existing flange joint. 
     While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.