Abstract:
A method of generating a comprehensive image ( 87 ) of interior surfaces ( 78, 80 ) of machine components such as a gas turbine combustor basket ( 59 ) and transition duct ( 34 ) by digitally stitching together multiple photographs ( 82 ) thereof, and analyzing the comprehensive image by contouring ( 91, 95 A-B) of colors and shadings thereon, and quantifying and tracking aspects of the contours (A, B, C) over time for indications of degradation ( 89 ) of the interior surfaces. A scope ( 58 ) may be inserted into a port ( 56 ) in the combustor with a camera ( 72, 74 ) in a rotatable end ( 70 ) of the scope for obtaining a circumferential set ( 84 ) of photos at each axial position along a length of the combustor and transition duct. A 3D surface scanning device ( 76 ) in the scope may define the geometry of the interior surface for 3D photographic modeling thereof providing a virtual walk-through inspection.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 13/972,000, filed 21 Aug. 2013 and published as US 2013/0335530 A1, which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to internal inspection of machinery, and more particularly to internal imaging and evaluation of power generating components including gas turbine combustor baskets and transition ducts. 
     BACKGROUND OF THE INVENTION 
     Internal surfaces of gas turbine combustors and transition ducts have been inspected using a scope camera inserted through the pilot nozzle port after removal of the pilot nozzle. This provides access for the scope through the center of the combustor cap into the combustion chamber basket and transition duct. However, previous camera inspection systems produce on the order of 300 individual photos of the interior surfaces of each combustor basket/transition. Position data may be stored with each image, but it is difficult and time consuming to make comparisons among these numerous small overlapping images in order to visualize the interior surface topography and any coloration or shading changes over larger areas than each individual photo. Visualization is complicated by the non-cylindrical shape of transition ducts, which causes image distortion from the angles of the inner surface relative to the camera. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a partial side sectional view of a gas turbine engine known in the art. 
         FIG. 2  is a perspective view of a transition duct known in the art. 
         FIG. 3  is side sectional view of an inspection scope inserted into a gas turbine combustor according to aspects of an embodiment of the invention. 
         FIG. 4  is side sectional view of an inspection scope inserted into a gas turbine combustor and transition duct according to aspects of an embodiment of the invention. 
         FIG. 5A  is a sequence of photos taken around the circumference of the interior surfaces of a combustor basket and transition duct at a given axial position. 
         FIG. 5B  is a circumferential panoramic image created by stitching the photos of  FIG. 5A  together. 
         FIG. 5C  is a series of circumferential panoramic images as in  FIG. 5B  taken at successive axial positions in the combustor basket and transition duct. 
         FIG. 5D  is a comprehensive image formed by stitching the circumferential panoramic images of  FIG. 5C  together. 
         FIG. 6  is a size history of three intensity contours tracked over time. 
         FIG. 7  is an enlarged side sectional view of the end of the scope of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       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 of the combustors  28  of a circular array of combustors in a can-annular arrangement 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  40  of the turbine section  26 , which includes stationary vanes and  38  rotating blades  40 . Compressor blades  42  are driven by the turbine blades  40  via a common shaft  41 . Fuel  42  enters each combustor via a central pilot fuel nozzle  43 , and via other supply tubes to a circular array of premix injectors. Compressed air  45  enters a plenum  46  around the combustors. It enters the upstream end  30  of the combustors, and is mixed with the fuel therein for combustion. The compressed air  45  also surrounds the combustors  28  and transition ducts  34  to provide cooling air thereto. It has a higher pressure than the combustion gas  36  in the combustor and in the transition duct. 
       FIG. 2  shows a transition duct  34  with an upstream end  48  that receives combustion gas  36  from the combustor. The upstream end  48  may be cylindrical. The downstream end  49  may be non-cylindrical such a generally rectangular. The duct body may have a substantial curvature  50 . 
       FIG. 3  is sectional side view of a combustor  28  with support legs  52 , between which compressed air  45  ( FIG. 1 ) enters to mix with fuel that is supplied to premix injectors  53  via fuel ports  54  in a mounting plate  55 . Some detail is omitted for clarity, including supply lines to the fuel ports. A central fuel port  56  receives a pilot fuel nozzle  43  ( FIG. 1 ), which is removed here. In its place, a camera boom or scope  58  is inserted for internal inspection of the combustor basket  59  and transition duct. Details of such camera systems are provided in the parent US patent application. 
     An inspection system housing  60  may be mounted to the pilot fuel port  56  by a mechanism normally used to mount the pilot fuel nozzle—for example by a threaded collar and/or machine screws  57 . A scope positioning drive  62  may include a scope rotation drive  63  and translation drive  64 . The rotation drive is optional if the distal end of the scope rotates as later described. A computer/controller  66  may control these drives. An interactive computer station  65  may provide operator control and computer graphics for human analysis. Control signal lines and power conductors may be provided through the interior of the scope. Control and power lines  67  may be provided to one or more cameras, lights, and distal actuators in the scope. Such lines  67  may include electrical conductors and, in some embodiments, optical fibers. The combustor  28  as shown is illustrated for reference, and is not a limitation except as claimed. 
       FIG. 4  is a sectional view of a scope  58  mounted as shown in  FIG. 3 , inserted into and through a combustor  28  and transition duct  34 . The scope may have one or more motor controlled articulations  68 , such as detailed in the parent US patent application. The end  70  of the scope may be rotatable by a motor  71  for scanning and imaging 360 degrees around the circumference of the inner surfaces  78 ,  80  at a given axial position. Herein “axial position” means a position along the axis  75  of the distal portion  70  of the inspection scope, which may substantially align with the 3D geometric centerline of the interior surfaces  78 ,  80  as much as possible. The end portion  70  may enclose a device such as camera  72 , and may further include a lens  74  such as a galvanometer actuated mirror that pivots on an axis normal to the axis  75  of the end  70  of the scope. One or more lights  76  may be provided for the camera. Other embodiments are taught in the parent US patent application. 
       FIGS. 5A-D  illustrate a process of stitching photos of the inner surfaces  78 ,  80  into a comprehensive view for analysis.  FIG. 5A  is a sequence or set  84  of photos  82  taken around the circumference of the interior surfaces of a combustor basket and transition duct at a given axial position.  FIG. 5B  is a circumferential panoramic image  86  created by stitching the photos  82  of  FIG. 5A  together.  FIG. 5C  is a series of circumferential panoramic  86  images as in  FIG. 5B  taken at successive axial positions in the combustor basket and transition duct.  FIG. 5D  is a comprehensive image  87  formed by stitching the circumferential panoramic images of  FIG. 5C  together and eliminating overlaps. This comprehensive image visually clarifies aspects of the surfaces that are unclear in the individual photos  82 . For example, darker shaded areas  88  may indicate normal carbon deposits. Lighter areas  89  within a dark area may indicate a hot spot where carbon is burned away. Although not visible in black and white, a diffuse yellow coloration is present, especially in the dashed area  91  shown, which may indicate oxidation. Another area  95 A has a slight blue tint with a slightly higher intensity in area  95 B. Such colorations and shadings may be contoured by computer for analysis. 
     An engineering model of the combustor assembly may be used to identify and image features caused by structures such as crosslink tubes  85 , acoustic damper holes  90 , and film cooling holes  92 , and subtract/ignore such features when creating surface contours  89 ,  90 ,  91 ,  95 A-B. Alternately, the structural features  85 ,  90 ,  92  may be contoured in addition to the surface contours so that changes in shape or position of the structures can be analyzed. Static analysis of the comprehensive image may be performed based on absolute intensity limits, contour gradient limits, contour jaggedness, and contour overlaps—for example, a white area overlapping grey or grey overlapping yellow. The contours may be tracked over successive inspections. Quantified aspects of the tracked contours may be graphed in a time series to show the rates and accelerations of degradation as later shown. This analysis may be used to adjust or preempt a maintenance schedule. In general, shading and colors may be analyzed to indicate wear and condition characteristics of the gas path surfaces, including any thermal barrier coating thereon. A jagged contour may indicate exfoliation or spelling of the thermal barrier coating due to age, environment, structural flaws, or overheating. 
     In another method utilizing the invention, a thermal indicator paint may be applied to the inner surfaces  78 ,  80  prior to assembling the combustor section, either in original production or after disassembly for maintenance. A test run of the engine may be performed for a limited time to bring the surfaces to operating temperatures. The engine may then be shut down, and the inner surfaces examined in accordance with the present invention. The thermal paint will then display the heat topography at the operating temperatures as a color topography. This indicates whether a new engine design, or a maintenance re-assembly, or a modification meets specifications for thermal limits, and if an engine is operating properly. By using the present invention, there is no need to disassemble the combustors to inspect the thermal paint response. Subsequently, after a period of engine operation, the thermal paint burns away, and the previously described time series of inspections may be performed without thermal paint. 
       FIG. 6  illustrates a time series of the sizes of three different intensity contours A, B, and C over a sequence of inspections. Contour A shows normal wear, Contour C shows no wear or degradation. Contour B shows a recent acceleration  89  in degradation above a predetermined acceleration threshold, causing an automated alert from the computer. The individual contours A, B, C may be identified and tracked over time using known algorithms, for example as used for weather radar tracking of storm cells and their intensities over time to compute local rainfall. The shapes of such contours may be quantified in terms of jaggedness, aspect ratio, or other factors. Such quantifications allow a high degree of automatic analysis that can bring timely attention to particular areas by computerized alerts, which may be presented for example as an audible alert and a flashing contour. 
       FIG. 7  shows an enlarged side sectional view of the distal end  70  of the scope  58  of  FIG. 4 . A camera sensor  72  such as a charge coupled device or other image sensor receives an image directed from a galvanometer-controlled mirror  74 . A light source  76  projects a pattern  92  onto the inner surface  80  of the transition duct  34  for surface definition by the computer/controller as described in the parent US patent application. A liquid crystal panel  93  in the light/projector  76 / 93  may define the pattern and alternately clear to allow non-patterned light to illuminate the surface for photography as in  FIG. 5A . Alternately, separate lights may be provided for pattern projection and photographic illumination. Surface scanning defines a precise surface contour relative to the camera for each image  82 . The surface  80  can be accurately reconstructed in three dimensions as a digital model by known pattern projection and triangulation between the projector and the receiving mirror or lens  74 . The photographic illuminating light may be white and/or a succession of different colors to enhance respective different aspects of the surface  80 . As an alternative to a pattern projector  93 , a triangulating laser surface scanner may be provided for defining the surface  80  in three dimensions. Such scanners can image a surface in 3 dimensions to a precision of tens of microns or thousandths of an inch, and thus can define surface roughness as an additional aspect of the comprehensive image for analysis. 
     By defining the surface relative to the camera, distortions due to camera angle can be removed by known algorithms. The surface image can then be transformed into a digital 3D visible surface rendering using known algorithms, allowing human inspectors to interactively “walk through” the combustor basket and transition duct via computer graphics for inspection, which may be color enhanced. An exemplary 3D scanning image processing software program is the “MeshLab” package of open source software that is downloadable via the Internet from the National Research Council of Italy Visual Computing Lab. Another source for exemplary 3D scanning image processing software is Geomagic of Research Triangle Park, N.C., USA. 
     In one embodiment, the comprehensive image may be mapped onto an engineering model of the interior surface to create a digital visual model of the interior surface in a computer for interactive walk-through viewing. Image distortions due to camera angle may be removed by defining the surface angles with a surface scanner as previously described and/or by fitting the comprehensive image to known surface features in the engineering model such as holes in the surface. 
     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.