Abstract:
Thermographic inspection of an internal component ( 28, 34 ) of power production equipment ( 20 ) by inserting an ultrasound energizer ( 74 A) into an inspection portal of the equipment to contact an exterior of the component, and inserting a camera scope via a second portal into an interior ( 52, 54 ) of the component. A motorized drive ( 66 ) may mount on a pilot fuel port ( 58 ) of a gas turbine to move the scope robotically within a combustor ( 28 ) and transition duct ( 34 ). A distal camera housing ( 69 ) on the scope pivots ( 64 ) and contains an infrared camera with a lateral field of view ( 85 ) that rotates about an axis  78  by rotating ( 73 ) a distal mirror head ( 70 ) on the housing or by rotating ( 73 ′) the housing ( 69 ′). Circumferential sets of thermographic images are acquired by rotating the field of view and translating it along a navigation path in the component interior.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to non-destructive internal inspection of installed power generating machinery, and more particularly to in-situ thermographic imaging of gas path inner surfaces of gas turbine combustor liners and transition ducts. 
       BACKGROUND OF THE INVENTION 
       [0002]    A common industrial gas turbine engine has a circular array of combustors. A transition duct channels combustion gas from each combustor to the first row of turbine blades. Combustion chambers and transition ducts commonly have metal inner liners for the combustion gas path. The inner surfaces of these liners have a thermal barrier coating (TBC), which may include one or more ceramic layers on a bond coat. The TBC is subject to wear and damage from cyclic thermal expansion, vibrations, heat, and particle impacts. The condition of the TBC is critical for protecting the gas path liners and other surrounding parts, so it is regularly inspected. This has been done by partly disassembling the engine. However, disassembly and reassembly is expensive and time-consuming, causing substantial down-time. It relieves installed stresses on components, thus modifying their in-situ shapes and clearances. It requires highly trained assembly technicians and relatively heavy equipment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The invention is explained in the following description in view of the drawings that show: 
           [0004]      FIG. 1  is a partial sectional side view of an upper half of a gas turbine engine known in the art. 
           [0005]      FIG. 2  is a sectional side view of a combustor and transition duct showing aspects of an embodiment of the invention. 
           [0006]      FIG. 3  is a sectional side view of a camera housing on an inspection scope positioned in the exit end of the transition duct. 
           [0007]      FIG. 4  is a sectional side view of a second embodiment of a camera housing on the inspection scope positioned in the exit end of the transition duct. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    The inventors recognized that thermographic inspection of the inner surfaces of gas turbine components in-situ would greatly reduce expense and down-time, would make more frequent inspection intervals feasible, and would extend the safe life of the components before replacement or repair. Herein, “in-situ” means the component being inspected remains installed in the engine. 
         [0009]      FIG. 1  is a partial side sectional view of a gas turbine engine  20  with a compressor section  22 , a combustion section  24 , and a turbine section  26  as known in the art. One combustor  28  of a circular array of combustors is shown. Each combustor  28  has an upstream end  30  and a downstream end  32 . A transition duct  34  and an exit piece  35  thereof transfer the combustion gas  36  from the combustor to the first row of airfoils of the turbine section  26 , which includes stationary vanes and 38 rotating blades  40 . Compressor blades  42  are driven by the turbine section via a common shaft  41 . Fuel  42  enters each combustor via a central pilot fuel nozzle  43 , and enters by tubes to a circular array of premix injectors. Compressed air  45  enters a plenum  46  around the combustors. It then enters the upstream end  30  of the combustor, and is mixed with the fuel therein for combustion. The compressed air  45  also surrounds the combustor  28  and transition duct  34  to cool them. It has a higher pressure than the combustion gas  36  in the combustor and in the transition duct. Maintenance access ports  47  are provided at various locations on the engine, including on the outer casing  39  of the combustion section as shown. 
         [0010]      FIG. 2  shows a combustor assembly  28  including a combustion chamber  50  mounted to a combustor cap  51  that is mounted inside a combustor outer casing  48 . The combustion chamber  50  and the transition duct  34  have inner surfaces  52 ,  54  coated with a thermal barrier coating (TBC), which commonly includes one or more ceramic layers on a bond coat. The pilot fuel nozzle  43  ( FIG. 1 ) has been removed from the pilot fuel nozzle port  58 , and an elongated inspection scope  56  is inserted in its place extending through the combustor cap  51 . A mounting tube  60  for the inspection scope may be mounted to the pilot fuel nozzle port  58  via a collar  62 . A computer  68  may control the scope robotically via a motorized drive  66  to extend into the combustor and to optionally rotate. Herein “robotically” means controllably operated by a computer along an automated predetermined navigation path and/or operated interactively under human direction via the computer. The scope may robotically articulate at a pivot joint  64  for example as taught in US patent application publication 2013/0335530A1, which is incorporated herein by reference. The scope may have a distal camera housing  69  with side-scanning infrared camera equipment. “Side-scanning” herein means the field of view  85  is substantially normal to the rotation axis  78 . The axis may coincide with, or be parallel to, a geometric axis of the camera housing. The camera housing can be moved automatically by the motorized scope along a predetermined navigation path. The camera housing  69  may have a rotatable head  70  containing a prism or mirror  71  that reflects image photons into a digital camera  72 . The head  70  may have an open port for the field of view  85 , or it may be made of an infrared transparent material or have a window of such material. 
         [0011]    The computer  68  may programmatically control an inspection process for detecting defects in the TBC by providing control signals to the motorized drive  66 , and to one or more acoustic transducers  74 A,  74 B. The computer  68  additionally receives input  76  from the camera  72 , and may perform processing thereon for TBC analysis. Processing may include digital stitching of the camera images into a panoramic view of the inner surfaces  52 ,  54 , contouring and analyzing thermal patterns thereon, and interactive display thereof for human view as taught for example in U.S. patent application Ser. No. 14/526,609 filed 29 Oct. 2014 (attorney docket number 2014P17920US), United States patent application publication number (to be determined), which is incorporated by reference herein. A technician may place one or more transducers  74 A,  74 B in contact with outer surfaces of the components  34 ,  50  at predetermined positions. Brackets  77  for transducer placement may be provided on the outer surfaces of the components  34 ,  50 . The transducer  74 A may be fastened to the bracket  77  to insure consistent acoustic coupling to the components across successive inspections, or an acoustic coupling material may be used. The inner surfaces  52 ,  54  can be thermographically inspected in-situ. A transducer  74 A may be re-positioned  74 B during the inspection process by stopping the imaging, moving the transducer, and restarting the imaging. The inspection does not limit each image to be taken directly under a transducer, since a transducer vibrates a portion of the component sufficiently to reveal flaws over an energized area around the transducer. 
         [0012]    A baseline panoramic thermographic scan may be compiled after initial installation of the gas turbine. During each subsequent thermographic inspection, the computer  68  may compile a panoramic scan, and may digitally subtract the original baseline scan or any previous scan from the current scan in order to expose changes that have occurred since the earlier scan. The changes may be contoured, quantified, and plotted in a time series to expose any acceleration in wear rates. Discontinuities in the TBC such as de-laminations, de-bonds, cracks, and spalling, as well as cracks in the metal substrates cause localized heating under ultrasound stimulation. This heating appears in the thermographic images, and can be enhanced by previous image subtraction. The panoramic image may be digitally projected onto a visible image or onto a 3-D model of the inner surface for display, allowing an interactive virtual walk-through inspection. 
         [0013]      FIG. 3  is sectional side view of an embodiment of the camera housing  69  of the inspection scope with a rotatable head  70  thereon positioned in the exit end of the transition duct  34 . The pivot joint  64  may be robotically controlled as known by an actuator  63  operating against a moment arm relative to a main pivot axis  67 . For example the actuator may act against a second pivot axis  65  offset from the main pivot axis  67 . The head  70  is rotatable about an axis  78 , which may coincide with, or be parallel with, a geometric centerline of the camera housing  69 . The computer may translate the head robotically along a path that substantially follows, or is parallel to, a geometric centerline of the interior surfaces  52 ,  54 . 
         [0014]    Head rotation  73  may be enabled for example by a hollow stepper motor  80  with powered stator  81  in the distal end  79  of the camera housing  69 , and a hollow unpowered rotor  83  with a hollow shaft  84  on which is mounted the head  70 . The stator coils may be powered and modulated by a wire  82  from the computer  68  ( FIG. 2 ). Such rotating head  70  requires no wires or cables, so it can rotate without limitation about an axis  78 . An alternate rotary drive means, not shown, is a servomotor or stepper motor in the distal end of the camera housing  69  with a pinion that drives an annular gear in the head  70 , which is mounted on a bearing of the camera housing. 
         [0015]    The head  70  has a prism or mirror  71  that redirects the lateral field of view  85  to the camera  72  through the hollow stepper motor  80 . The camera  72  may use fixed focus, or a known automatic focusing method, or it may be focused by the computer  68  based on the known position of the head  70  relative to a 3-dimensional virtual model of the interior surfaces  52 ,  54 . Alternately, the sensor of the camera may be replaced with a bundle of infrared optical fibers, not shown, that transmits the image through the inspection scope to an external camera. A circumferential set of thermographic images can be acquired at each one of a sequence of axial positions along the interior surfaces  52 ,  54  by rotation of the head  70 . Optionally the head can be rotated and translated proportionally to provide a helical scan of the inner surfaces  52 ,  54 . 
         [0016]      FIG. 4  is a sectional side view of another embodiment of a camera housing  69 ′ positioned in the exit end of the transition duct  34 . This camera housing  69 ′ rotates about an axis  78 ′, which may substantially coincide with a geometric centerline of the camera housing. Rotation can be enabled, for example, by a stepper motor  80  in a pivot hub  86  attached to the pivot joint  64 . The stepper motor may have a hollow unpowered rotor  83 , a hollow shaft  84 , and a stator  81  powered by a conductor wire  82 . Alternately, rotation of the housing may be provided by a servomotor or stepper motor in the pivot hub  86  with a pinion that drives an annular gear in a proximal end of the housing  69 ′, which housing is mounted on a bearing of the pivot hub  86 . An infrared camera  72 ′ is mounted in the camera housing  69 ′ with a field of view  85  oriented normally to the rotation axis  78  for thermographic imaging of the interior surface  54 . 
         [0017]    During rotation of the camera housing  69 ′, the camera  72 ′ acquires a circumferential set of thermographic images, and transmits them via connection wire  76  to the computer  68  ( FIG. 2 ). The computer controls the inspection scope robotically to translate the camera housing  69 ′ along a path that substantially follows, or is parallel to, a geometric centerline of the inner surfaces  52 ,  54 . The camera housing  69 ′ may rotate in alternating directions to acquire a sequence of circumferential sets of thermographic images covering the interior surfaces  53 ,  54 . The camera connection wire  76  may be coiled to tolerate repeated alternating rotations. Rotation is not needed more than 180 degrees in each direction from a neutral position for each circumferential scan. 
         [0018]    The camera  72 ′ may be a known type such as a USB infrared or multi-spectral camera with fixed focus, or an auto-focus technology such as contrast detection or phase detection. Alternately, the camera  72 ′ may be remotely focused by the computer  68  based on the known position of the camera relative to a 3 dimensional virtual model of the inner surfaces  52 ,  54 . Optionally, a focus-assist lamp or focus spot projector may be provided to assist in focusing. Alternately, a visible-spectrum camera (not shown) mounted parallel to the imaging camera  72 ′ may focus with visible technology and provide focus control to the infrared imaging camera  72 ′. 
         [0019]    Alternately to the embodiments shown in  FIGS. 3 and 4 , a side scanning infrared camera may be added to any of the camera housing embodiments shown in US patent application publication 201310335530A1. Such a combined inspection scope provides coordinated visible and thermographic scanning after cool-down of the engine without disassembly thereof. 
         [0020]    Applying the ultrasound to the outer surfaces of the components  34  and  50  instead of the inner surfaces eliminates damage to the TBC caused by contact with the transducer, and eliminates the need for ultrasound elements in the camera housing  69 . Moreover, acoustic coupling to the uncoated metal surface may be more effective than to the ceramic coating surface, and lateral dissemination of the acoustic energy through the metal to an entire inspection region is not affected by engine-specific flaws in the ceramic coating. No disassembly of the engine is required other than removing the pilot nozzle  43  and opening an inspection port  47 . The outer casing  39  can remain installed around the combustion section. 
         [0021]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.