Abstract:
A device for measuring internal clearances includes a base having a base surface. A first leg in sliding engagement with the base includes a first leg surface and a first distal end. When the base surface abuts a component, a predetermined distance between the base surface and the first leg surface results in the first distal end being located in the clearance. A method for measuring a clearance includes inserting a leg of a device into a borehole and moving the device rearward until the device abuts the borehole. The method further includes withdrawing the leg from the borehole, extending the leg in the clearance, and measuring the distance that the leg was extended after being withdrawn.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to measuring internal clearances. Specifically, the present invention describes a device and method for measuring internal clearances, for example in a turbine, in which the clearance to be measured is not directly accessible. 
     BACKGROUND OF THE INVENTION 
     Large pieces of commercial equipment often have fixed components in close proximity with moving components. In a gas turbine, for example, a compressor includes multiple stages of rotating blades in close proximity with stationary vanes. Ambient air enters the compressor, and the rotating blades and stationary vanes progressively impart kinetic energy to the working fluid (air) to increase the pressure of the working fluid and bring it to a highly energized state. The compressed working fluid flows to one or more combustors which mix fuel with the compressed working fluid and ignite the mixture to produce combustion gases having a high temperature and pressure. The combustion gases flow through alternating stages of rotating blades or buckets and fixed blades or nozzles in the turbine. The rotating blades or buckets are attached to a rotor, and expansion of the combustion gases as they flow through the turbine stages cause the buckets, and thus the rotor, to rotate to produce work. 
     The clearance between the rotating and stationary components in the compressor and turbine is an important design and operational consideration that balances efficiency and performance on the one hand with manufacturing and maintenance costs on the other hand. For example, reducing the clearance between the buckets and the static shroud or casing in the turbine generally improves the efficiency and performance of the turbine by reducing the amount of combustion gases that bypass the turbine buckets. However, reduced clearances may also result in additional manufacturing costs to achieve the reduced clearances and increased maintenance costs attributed to increased rubbing, friction, or impact between the rotating and stationary components. 
     The clearances between rotating and stationary components are often checked during assembly and periodically after operations to ensure that the design clearances are maintained and the components are properly aligned. During assembly, the rotating and stationary components may be readily accessible to verify clearances. However, once assembled, the rotating and stationary components may not readily accessible. As a result, extended shutdown periods to allow for time-consuming disassembly of the components may be necessary to gain direct access to the clearances to be measured. Alternately, the clearances may be indirectly measured by measuring adjacent components. However, indirect measurement of the clearances introduces error in the measurements, and the introduced errors may be significant in comparison to the allowable or desired clearances. Therefore, a device for directly measuring clearances between rotating and stationary components in assembled equipment would be desirable. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     One embodiment of the present invention is a device for measuring a clearance between an inner portion of a turbine casing and an outer portion of a turbine bucket. The device includes a base having a base surface. A first leg in sliding engagement with the base includes a first leg surface and a first distal end. When the base surface abuts the turbine casing, a predetermined distance between the base surface and the first leg surface results in at least a portion of the first distal end of the first leg being located between the inner portion of the turbine easing and the outer portion of the turbine bucket. 
     An alternate embodiment of the present invention is a device for measuring a clearance between an inner portion of a turbine casing and an outer portion of a turbine bucket. The device includes a base having a base surface. A first leg in sliding engagement with the base includes a first leg surface and a first distal end. A second leg proximate to the base includes a second distal end. When the base surface abuts the turbine casing, a predetermined distance between the base surface and the first leg surface results in at least a portion of the first distal end of the first leg being located between the inner portion of the turbine casing and the outer portion of the turbine bucket and the second distal end of the second leg being approximately even with the inner portion of the turbine casing. 
     The present invention also includes a method for measuring a clearance between an inner portion of the turbine casing and an outer portion of a turbine bucket. The method includes inserting a leg of a device into a borehole in the turbine casing and moving the device rearward until the device abuts the borehole in the turbine casing. The method further includes withdrawing the leg of the device from the borehole until at least a portion of the leg abuts the inner portion of the turbine casing, extending the leg of the device inside the turbine casing until at least a portion of the leg abuts the outer portion of the turbine bucket, and measuring the distance that the leg was extended after being withdrawn. 
     Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying Figures, in which: 
         FIG. 1  is a simplified cross-section of an outer portion of a turbine stage; 
         FIG. 2  is an enlarged view of a clearance between a shroud tip and an inner portion of a turbine casing; 
         FIG. 3  is a side plan view of a measuring device according to one embodiment of the present invention; 
         FIG. 4  is a front plan view of the measuring device shown in  FIG. 3 ; 
         FIG. 5  is a simplified cross-section of the measuring device shown in  FIGS. 3 and 4  inserted through a borehole in the turbine casing; 
         FIG. 6  is an enlarged view of the distal end of the measuring device shown in  FIG. 5 ; 
         FIG. 7  is a side plan view of a measuring device according to an alternate embodiment of the present invention; 
         FIG. 8  is a front plan view of the measuring device shown in  FIG. 7 ; 
         FIG. 9  is a simplified cross-section of the measuring device shown in  FIGS. 7 and 8  inserted through a borehole in the turbine casing; 
         FIG. 10  is an enlarged axial cross section of the first and second members shown in  FIG. 9 ; and 
         FIG. 11  is an enlarged view of the distal end of the measuring device shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. 
     Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  provides a simplified cross-section of an illustrative environment for various embodiments of the present invention. Although various embodiments of the present invention are illustrated in the context of a turbine stage, one of ordinary skill in the art should readily appreciate that the scope of the present invention is not limited to measuring clearances in a turbine stage and is properly defined by the structural limitations of the device recited in the claims. As shown in  FIG. 1 , an outer portion of a turbine stage typically includes a turbine casing  10  that surrounds the stage and contains the combustion gases as they flow through the turbine. The turbine casing  10  may be a single piece or unitary construction, or it may comprise an outer shell  12  surrounding an inner shell  14 , as shown for example in  FIG. 1 . Boreholes  16  may be peripherally located around the turbine casing  10  to provide internal access to the turbine without requiring substantial disassembly. 
     Each turbine stage further includes a row of rotating blades or buckets  18 . The outer portion of each bucket  18  may include one or more shroud tips  20 . The shroud tips  20  extend radially from the buckets  18 , producing a clearance  22  between the shroud tips  20  at the outer portion of the buckets  18  and an inner portion of the turbine casing  24 , as more clearly illustrated in  FIG. 2 . As shown in  FIGS. 1 and 2 , the shroud tips  20  may not be axially aligned with the boreholes  16  that pass through the turbine casing  10 . As a result, the clearance  22  between the shroud tips  20  at the outer portion of the buckets  18  and the inner portion of the turbine casing  24  may not be directly visible or observable through the boreholes  16 , making direct measurement of the clearance  22  difficult without disassembly of the turbine casing  10 . 
       FIG. 3  is a side plan view and  FIG. 4  is a front plan view of a measuring device  30  according to one embodiment of the present invention. As shown in  FIGS. 3 and 4 , the device  30  generally includes a base  32  and a first leg  34 . The base  32  is sized according to the size of the boreholes  16  in the turbine casing  10 . For example, the height of the base  32  may be 4 inches, 6 inches, 8 inches, or longer to accommodate corresponding borehole  16  sizes. The effective width or diameter of the base  32  may be sized to prevent the base  32 , and thus the first leg  34 , from extending too far into the turbine and contacting sensitive portions of the turbine bucket  18 . In addition, the base  32  includes a base surface  36  which may be curved or shaped to provide a complementary fit with the boreholes  16 . 
     The first leg  34  includes a first distal end  38 , and in particular embodiments, the first leg  34  may include a first member  40  that extends substantially perpendicular from the first distal end  38  of the first leg  34 . The first leg  34  may be in sliding engagement with the base  32 . For example, as shown in  FIGS. 3 and 4 , pins  42  may connect the first leg  34  to the base  32 , and slots  44  in the base  32  may allow the first leg  34  to slide with respect to the base  32 . In alternate embodiments, a rail or other equivalent structure between the first leg  34  and the base  32  may be used to allow the first leg  34  to move with respect to the base  32 . As a result of this sliding engagement between the first leg  34  and the base  32 , the first distal end  38  of the first leg  34  may be extendable along and away from the base  32 . The first leg  34  may also be biased in a particular direction with respect to the base  32 . For example, as shown most clearly in  FIG. 3 , the first leg  34  may include a tab  46 , and a spring  48  between the base  32  and the tab  46  may be used to bias the first leg  34  upward with respect to the base  32 . 
     The first leg  34  further includes a first leg surface  50  on either side of the first leg  34 . Although  FIG. 3  arbitrarily indicates the first leg surface  50  on the right side of the first leg  34 , such is not a limitation of the embodiments of the present invention unless specifically cited in the claims, and the first leg surface  50  may alternately comprise the left side of the first leg  34 . The first leg surface  50  is a predetermined distance  52  from the base surface  36  so that when the base surface  36  abuts the turbine casing  10  at least a portion of the first distal end  38  of the first leg  34  (e.g., the first member  40 , if present) is located between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . The predetermined distance  52  between the first leg surface  50  and the base surface  36  may be adjustable to accommodate specific geometries and dimensions of the clearance  22  being measured. For example, the diameter and depth of the boreholes  16 , the thickness of the turbine casing  10 , and/or the axial offset between the clearance  22  being measured and the corresponding borehole  16  are all examples of specific geometries and dimensions that may require adjustment of the predetermined distance  52  between the first leg surface  50  and the base surface  36  to ensure that at least a portion of the first distal end  38  of the first leg  34  is located between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18  when the base surface  36  abuts the turbine casing  10 . Various means may be used to adjust the predetermined distance  52 . For example, the pins  42  previously described with respect to  FIGS. 3 and 4  may be in a threaded engagement  54  between the base  32  and the first leg  34  so that rotation of the pins  42  in either direction alternately increases or decreases the predetermined distance  52  between the base  32  and the first leg  34 . Other structures for adjusting the predetermined distance  52  between the base  32  and the first leg  34  may include, for example, clamps, screws, washers, and other equivalent structure known to one of ordinary skill in the art. 
       FIG. 5  provides a simplified cross-section of the measuring device  30  shown in  FIGS. 3 and 4  inserted through the borehole  16  in the turbine casing  10 . As shown in  FIG. 5 , the device  30  is illustrated measuring the internal clearance  22  between the inner portion of the casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . To do so, the first leg  34  of the device  30  is inserted through the borehole  16  in the turbine casing  10 , and the device  30  is moved rearward until the base surface  36  abuts or touches the turbine casing  10 . In this position, the predetermined distance  52  between the base surface  36  and the first leg surface  50  ensures the proper positioning of at least a portion of the first distal end  38  in the clearance  22  between the inner turbine casing  24  and the shroud tip  20 . Specifically, with the base surface  36  abutting or touching the turbine casing  10 , the first distal end  38  of the first leg  34  extends through the borehole  16  until it is approximately even with the inner portion of the turbine casing  24  resulting in at least a portion of the first distal end  38  being located between the inner portion of the turbine casing  24  and shroud tip  20  at the outer portion of the turbine bucket  18 . The first member  40 , if present, would thus extend substantially perpendicular from the first distal end  38  along the inner surface of the casing  24 . With at least a portion of the first distal end  38  of the first leg  34  between the inner portion of the turbine casing  24  and shroud tip  20  at the outer portion of the turbine bucket  18 , the clearance  22  between the inner portion of the turbine casing  24  and the outer portion of the turbine bucket  18  may be measured by slightly withdrawing the device  30  from the borehole  16  or alternately sliding the first leg  34  with respect to the base  32  to ensure the first distal end  38  contacts the inner portion of the turbine casing  24 . The first leg  34  may then be slid in the opposite direction along and away from the base  32  until the first distal end  38  contacts the shroud tip  20 , as shown more clearly in  FIG. 6 . An indicator  56  may be connected to the first leg  34  to measure the distance traveled by the first leg  34 , and thus the clearance  24  between the inner portion of the turbine casing  24  and shroud tip  20  at the outer portion of the turbine bucket  18 . 
       FIGS. 7 and 8  show a measuring device  60  according to an alternate embodiment of the present invention. In this embodiment, the device  60  generally includes a base  62 , a first leg  64 , and a second leg  66 . The base  62  again is sized according to the size of the boreholes  16  in the turbine casing  10 . For example, the height of the base  62  may be 4 inches, 6 inches, 8 inches, or longer to accommodate corresponding borehole  16  sizes. The effective width or diameter of the base  62  may be sized to prevent the base  62 , and thus the first and second legs  64 ,  66 , from extending too far into the turbine and contacting sensitive portions of the turbine bucket  18 . In addition, the base  62  includes a base surface  68  which may be curved or shaped to provide a complementary fit with the boreholes  16  through the turbine casing  10 . 
     The first leg  64  includes a first distal end  70 , and in particular embodiments, the first leg  64  may include a first member  72  that extends substantially perpendicular from the first distal end  70  of the first leg  64 . The first leg  64  is in sliding engagement with the base  62 , either directly or indirectly through sliding engagement with the second leg  66 . For example, as shown in  FIGS. 7 and 8 , pins  74  may connect the first leg  64  to the second leg  66 , and slots  76  in the second leg  66  may allow the first leg  64  to slide with respect to the second leg  66 , and thus the base  62 . In alternate embodiments, a rail or other equivalent structure between the first leg  64  and the second leg  66  may be used to allow the first leg  64  to move with respect to the second leg  66  and the base  62 . The first leg  64  may be biased in a particular direction with respect to the base  62 . For example, as shown most clearly in  FIG. 7 , the first leg  64  may include a tab  78 , and a spring  80  between the second leg  66  and the tab  78  may be used to bias the first leg  64  upward with respect to the base  62 . As a result of this sliding engagement between the first leg  64  and the second leg  66  and base  62 , the first distal end  70  of the first leg  64  may be extendable along and away from the base  62 . 
     The first leg  64  further includes a first leg surface  82  on either side of the first leg  64 . Although  FIG. 7  arbitrarily indicates the first leg surface  82  on the right side of the first leg  64 , such is not a limitation of the embodiments of the present invention unless specifically cited in the claims, and the first leg surface  50  may alternately comprise the left side of the first leg  34 . The first leg surface  82  is a predetermined distance  84  from the base surface  68  so that when the base surface  68  abuts the turbine casing  10  at least a portion of the first distal end  70  of the first leg  64  (e.g., the first member  72 , if present) is located between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . The predetermined distance  84  between the first leg surface  82  and the base surface  68  may be adjustable to accommodate specific geometries and dimensions of the clearance  22  being measured. For example, the diameter and depth of the borehole  16 , the thickness of the turbine casing  10 , and/or the axial offset between the clearance  22  being measured and the corresponding borehole  16  are all examples of specific geometries and dimensions that may require adjustment of the predetermined distance  84  between the first leg surface  82  and the base surface  68  to ensure that at least a portion of the first distal end  70  of the first leg  64  is located between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18  when the base surface  68  abuts the turbine casing  10 . Various means may be used to adjust the predetermined distance  84 . For example, screws  86  may provide a threaded engagement  88  between the base  62  and the first leg  64  and/or the second leg  66  so that rotation of the screws  86  in either direction alternately increases or decreases the predetermined distance  84  between the base  62  and the first leg  64 . Other structures for adjusting the predetermined distance  84  between the base  62  and the first leg  64  may include, for example, clamps, screws, washers, and other equivalent structure known to one of ordinary skill in the art. 
     The second leg  66  includes a second distal end  90 , and in particular embodiments, the second leg  66  may include a second member  92  that extends substantially perpendicular from the second distal end  90  of the second leg  66 . The second leg  66  is generally proximate the base  62  and may be in sliding engagement with the base  62 . For example, as shown in  FIGS. 7 and 8 , the previously described screws  86  may connect the second leg  66  to the base  62 , and slots  94  in the base  62  may allow the second leg  66  to slide with respect to the base  62 . In alternate embodiments, a rail or other equivalent structure between the second leg  66  and the base  62  may be used to allow the second leg  66  to move with respect to the base  62 . As a result of this sliding engagement between the second leg  66  and the base  62 , the second distal end  90  of the second leg  66  may be extendable along and away from the base  62 . In this manner, the second leg  66  may be adjusted to vary the distance between the second distal end  90  and the base  62  to allow the device  60  to be used to measure components having different dimensions. 
       FIG. 9  provides a simplified cross-section of the measuring device  60  shown in  FIGS. 7 and 8  inserted through the borehole  16  in the turbine casing  10 . As shown in  FIG. 9 , the device  60  is illustrated measuring the internal clearance  22  between the inner portion of the casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . To do so, the first and second legs  64 ,  66  of the device  60  are inserted through the borehole  16  in the turbine casing  10 , and the device  60  is moved rearward until the base surface  68  abuts or touches the turbine casing  10 . In this position, the predetermined distance  84  between the base surface  68  and the first leg surface  82  ensures the proper positioning of at least a portion of the first distal end  70  in the clearance  22  between the inner turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . Specifically, with the base surface  68  abutting or touching the turbine casing  10 , the first distal end  70  of the first leg  64  extends through the borehole  16  until it is approximately even with the inner portion of the turbine casing  24  resulting in at least a portion of the first distal end  70  being located between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . The first member  72 , if present, would thus extend substantially perpendicular from the first distal end  70  along the inner surface of the turbine casing  24 . Similarly, with the base surface  68  abutting or touching the turbine casing  10 , the second distal end  90  of the second leg  66  extends through the borehole  16  until it is approximately even with the inner portion of the turbine casing  24 . The second member  92 , if present, would thus extend substantially perpendicular from the second distal end  90  along the inner surface of the turbine casing  24 . If desired, the first and second members  72 ,  92 , if present, may be nested in one another to minimize the combined height of the first and second members  72 ,  92 , as shown for example in the axial cross section of the first and second members  72 ,  92  illustrated in  FIG. 10 . 
     With at least a portion of the first distal end  70  of the first leg  64  between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 , the clearance  22  between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18  may be measured by slightly withdrawing the device  60  from the borehole  16  or alternately sliding the first and second legs  64 ,  66  with respect to the base  62  until the first and second distal ends  70 ,  90  are approximately even with the inner portion of the turbine casing  24  and at least a portion of the first distal end  70  is located between the inner portion of the turbine casing  24  and the outer portion of the turbine bucket  18 . In this position, the second member  92 , if present, contacts the inner portion of the turbine casing  24 , as shown more clearly in  FIG. 11 . The first leg  64  may then be slid along and away from the base  62  until at least a portion of the first distal end  70  (e.g., the first member  72 , if present) contacts the shroud tip  20 , as shown more clearly in  FIG. 11 . An indicator  96  may be connected to the first leg  64  to measure the distance traveled by the first leg  64 , and thus the clearance  22  between the inner portion of the turbine casing  24  and the shroud tip  20  at the outer portion of the turbine bucket  18 . 
     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 the claims if they include 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 languages of the claims.