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.
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.
The invention is explained in the following description in view of the drawings that show:
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.
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 74A, 74B. 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 74A, 74B 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 74A 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 74A may be re-positioned 74B 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.
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.
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 (
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.
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 (
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′.
Alternately to the embodiments shown in
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.
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.