Abstract:
Turbine engine casing interiors are visually inspected in a fully assembled turbine casing by mounting an optical camera on a turbine blade that captures optical images, such as of the casing abradable surface. Optical images are recorded as the blade circumferentially sweeps the turbine casing when the turbine is operated in turning gear mode or manually rotated. Blade rotational position data are collected by a rotational position sensor. A data processing system correlates the captured optical images and rotational position data about the turbine casing circumference. This method and apparatus provide an accurate and cost effective solution for accessing a turbine casing interior.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending and now allowed, commonly owned at time of filing, United States utility patent application entitled “IN SITU BLADE-MOUNTED TIP GAP MEASUREMENT FOR TURBINES”, filed on Oct. 2, 2013 and assigned Ser. No. 14/043,913, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to in-situ optical inspection of steam or gas turbine engine casing interiors—for example in turbine sections, or in the case of a gas turbine engines also its compressor section—such as for inspection of the circumscribing turbine engine casing ring segment. More particularly, embodiments of the invention relate to in-situ optical inspection by mounting a radially oriented optical camera directly on a turbine blade while in-situ within an industrial gas turbine engine and rotating the rotor so that the blade sweeps at least a portion of the circumscribing turbine casing ring segment in either the compressor or hot gas turbine sections. In other embodiments of the invention the entire circumference of the circumscribing casing ring segment is swept by rotating the rotor while the industrial gas turbine is operated in turning gear mode. Images captured by the sweeping camera field of view are then available for further inspection analysis. 
     2. Description of the Prior Art 
     During assembly and at periodic times throughout the life of a gas turbine blade tip clearances must be measured or the turbine casing interior requires visual inspection. Proper tip clearance enables better efficacy of gas turbines and lowers harmful emissions. To date there are ways of measuring tip clearances, but the methods requiring the removal of the upper casing that circumscribes the turbine blade tips during measurement, limiting the number of inspection points, or taking a relatively long time to complete. 
     There are typically two known common methods for measuring blade tip clearances. In the first method the measurement of tip clearance is typically accomplished by removing the turbine or compressor case upper half to provide access to the blades. Shims are then inserted between the blades tips and the flow path side or ring segments of the lower case at the horizontal joint. Measurements are typically taken at the leading and trailing edge sides of the blade tips for every blade. These measurements are referred to as half shell measurements. This method provides very little accuracy or reproducibility because the lower case tends to change shape without the upper case in place. Also, the half shell measurement locations are not necessarily representative of the local case shape at all angular rotational positions about the entire rotational surface swept by the turbine blade. 
     The second known common method for measuring blade tip clearances is by opening an inspection port in the side of the engine that is aligned with the blade path. A contact or non-contact probe is inserted into the port to measure the distance of the blade tip from the gas path side of the case or ring segments. There are a limited number of these inspection ports oriented about the turbine casing. Therefore only data from select rows and cord positions can be obtained. Furthermore, as noted above in the description of the first known inspection method the inspection locations may not be representative of the casing shape about the entire rotational circumference of the turbine. In some spots, due to casing shape disparities there may be varying tip gap. 
     Thus, a need exists for a method to measure turbine blade tip clearances in-situ within an assembled turbine without removing part of the turbine casing that circumscribes the blade tips. 
     A need also exists for a method to measure turbine blade tip clearances in-situ within an assembled turbine casing, so that localized blade tip gap differences can be identified and measured. 
     An additional need exists for a method to determine whether the turbine rotor assembly is aligned within its circumscribing turbine casing, so that alignment can be adjusted to assure rotor rotational axis concentricity within the casing. For example, so that turbine vane carriers are centered to the rotor during alignment verification. 
     Another need exists for a method to inspect the interior of the assembled turbine casing visually about the entire blade rotational circumference. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of some embodiments that are described herein is to measure turbine blade tip clearances in-situ within an assembled turbine without removing part of the turbine casing that circumscribes the blade tips. 
     It is also an object of some embodiments described herein to measure turbine blade tip clearances in-situ within an assembled turbine casing, so that localized blade tip gap differences can be identified and measured. 
     An additional object of some embodiments described herein is to determine whether the turbine rotor assembly is aligned within its circumscribing turbine casing, so that alignment can be adjusted to assure rotor rotational axis concentricity within the casing, including but not limited to turbine vane carriers/rotor centering during alignment verification. 
     An object of the present invention is to inspect the interior of the assembled turbine casing visually about the entire blade rotational circumference. 
     These and other objects are achieved in accordance with embodiments of the present invention by using the blade (not the case) as the carrier for a visual inspection camera without removing the cover as is traditionally done. In some embodiments an optical camera is mounted on a blade to capture images within the turbine case during blade rotation. In addition, a digital inclinometer or gyroscope is used to relate each measurement to an angular rotational clock position around the rotor by measuring the blade orientation with respect to gravitational pull or a reference position. Alternatively angular position can be determined by a sensor that monitors the rotor rotational position or any other sensor location that is coupled to the turbine. The optical inspection system is delivered to the blade location by a flexible snake arm delivered from the inlet or exhaust of • the unit or through an existing inspection port. The camera apparatus and its data acquisition system are coupled to the specified blade using a mechanical, magnetic, or adhesive gripping mechanism. The delivery snake arm is removed and the system logs displacement and rotational data as the rotor rotates. To retrieve the data acquisition system the arm is again inserted to deactivate the griping mechanism and retrieve the data acquisition system. Data collected can be either stored the data acquisition system internal storage, removable media, or can be streamed wirelessly in real time during measurement. Data collected can also be communicated via a direct cable connection. When blade tip gap measurement apparatus are added to or substituted for the visual inspection camera, the insertion method and blade gripping mechanism also provide an accurate and cost effective solution for accessing turbine casing deformation impact on blade tip clearance and rotor/casing alignment. In tip gap measurement embodiments, using the blade as the measurement instrument carrier enables the measurement of the tip clearance of a particular blade along the entire path it makes during one or more revolutions in the engine on turning gear. Embodiments of this method of tip clearance measurement include a contact or non-contact displacement sensor coupled with a data acquisition system to record the measured displacement between the blade and the corresponding circumscribing turbine casing (e.g., the gas path side of the case or the ring segments). 
     More particularly, embodiments of the invention feature a method for in-situ visual inspection of a turbine engine casing interior, by providing a gas turbine with a rotatable rotor having a turbine blade with a radially outwardly projecting tip in opposed spaced relationship with a circumscribing turbine casing, defining a gap there between. At least one optical camera is coupled to the turbine blade. The camera is capable of capturing camera images in its field of view and generating a camera image data set. A rotor rotational position sensor is coupled to the turbine. The rotor is rotated so that the turbine blade tip sweeps at least a portion of the circumscribing turbine casing while generating the image data set with the camera and a rotational position data set with rotational position sensor. The image and rotational position data sets are acquired with a data acquisition system that is coupled to the camera and the rotational position sensor. Camera image relative to rotational position is correlated with the image and rotational data sets in a data analyzer system that is coupled to the data acquisition system. 
     Other embodiments of the invention feature a method for in-situ visual inspection of a turbine engine casing interior, by providing a turbine engine with a rotatable rotor having a turbine blade with a radially outwardly projecting tip in opposed spaced relationship with a circumscribing turbine casing, defining a gap there between. At least one optical camera is coupled to the turbine blade. The camera is capable of capturing camera images in its field of view and generating a camera image data set. The rotor is rotate, so that the turbine blade tip sweeps at least a portion of the circumscribing turbine casing while generating the image data set with the camera. 
     Additional embodiments of the invention feature a system for in-situ visual inspection of a turbine engine casing interior, comprising at least one optical camera that is capable of capturing camera images in its field of view and generating a camera image data set, coupled to the turbine blade. A rotor rotational position sensor that is capable of generating a data set of blade rotational position is coupled to the turbine. A data acquisition system is coupled to the camera and the rotational position sensor, for acquiring the image and rotational position data sets during rotor rotation as the turbine blade tip sweeps at least a portion of the circumscribing turbine casing. A data analyzer system is coupled to the data acquisition system, for correlating with the image and rotational data sets with camera image relative to rotational position. 
     The objects and features of the present invention may be applied jointly or severally in any combination or sub-combination by those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an elevational schematic view of an embodiment of a turbine tip gap clearance measurement system, coupled to a turbine engine, including a blade mounted instrument system with a probe system and a data acquisition system that are communicatively coupled to a data processing system outside the turbine via a wireless communication system; 
         FIG. 2  is a detailed schematic view of an embodiment of a probe system, including displacement sensors, coupled to a turbine blade; 
         FIG. 3  is an elevational schematic view of another embodiment of a turbine tip gap clearance measurement system coupled to a turbine, including a blade mounted instrument system with a probe system and a data acquisition system that are communicatively coupled to a data processing system outside the turbine via a portable data storage device transferred from the blade mounted instrument system to a data processing system interface for downloading to the data processing system personal computer; 
         FIG. 4  is an elevational schematic view of another embodiment of a turbine tip gap clearance measurement system coupled to a turbine, including a blade mounted instrument system with a probe system and a data acquisition system that are communicatively coupled to a data processing system outside the turbine via a cable; 
         FIG. 5  is a detailed elevational schematic view of an embodiment of a retaining strap for mounting an inspection system of the invention to a turbine blade, having mating hook and loop fasteners; 
         FIG. 6  is a detailed elevational schematic view of an embodiment of a retaining clamp for mounting an inspection system of the invention to a turbine blade, having opposed plates that are compressively coupled to a turbine blade circumference by screws; 
         FIG. 7  is a perspective elevational view of an embodiment of a blade mounted instrument that is magnetically coupled to a turbine blade; 
         FIGS. 8 and 9  are elevational schematic view of an embodiment of a turbine tip gap clearance measurement system coupled to a turbine, including a blade mounted instrument system with a contact displacement probe system and a data acquisition system that are communicatively coupled to a data processing system outside the turbine via a wireless communication system; and 
         FIGS. 10 and 11  are elevational schematic views of an embodiment of a turbine tip gap clearance measurement system of the invention coupled to a turbine, including a blade mounted instrument system with a probe system, an optical camera inspection system, and a data acquisition system that are communicatively coupled to a data processing system outside the turbine via a wireless communication system. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     After considering the following description, those skilled in the art will clearly realize that the teachings of the invention can be readily utilized in methods and apparatus for in-situ visual inspection of steam or gas turbine interiors, including the blade tip gap between rotating blades and the circumscribing turbine casing (e.g., the ring segments or gas paths defined within the casing), using the blade (not the case) as the reference measurement location without removing the cover as is traditionally done. This enables visual inspection within the turbine interior along the entire blade path as the camera-mounted blade revolves in the engine on turning gear or by manual shaft manipulation. The inspection system can be moved from blade to blade or blade row to blade row, so that visual inspection data can be obtained for a plurality of or all of the blade rows about their full 360 degree rotational sweep. By performing the visual inspection, with or without tip gap measurements, on a fully assembled turbine casing the gathered information is indicative of the actual structural condition and/or blade tip clearances experienced by an operational turbine, including any potential mechanical or thermal distortions imparted on the casing structure after its assembly. Also, after sufficient cool down of an in-service engine, pre-rebuild visual condition inspection and/or tip gap measurements can be obtained for service diagnostic evaluation and to obtain pre-rebuild baseline clearance information suitable for “before” and “after” rebuild evaluation and documentation. 
     Embodiments of this system and method for turbine casing interior visual inspection include an optical camera, with internal or external image data acquisition or recording system that is mounted on a blade to capture images within the turbine case during blade rotation. In embodiments also incorporating tip gap measurement capabilities, a contact or non-contact displacement sensor is coupled with a data acquisition system to record the measured displacement between the blade and the corresponding circumscribing turbine casing (e.g., the gas path side of the case or the ring segments). In addition, a digital inclinometer or gyroscope is used to relate each measurement to an angular rotational clock position around the rotor by measuring the blade orientation with respect to gravitational pull or a reference position. Alternatively angular position can be determined by a sensor that monitors the rotor rotational position or any other sensor location that is coupled to the turbine. The visual inspection system of the invention, with or without the blade tip gap measurement system, is delivered to the blade location by a flexible snake arm delivered from the inlet or exhaust of the unit or through an existing inspection port. The visual image camera system, the optional gap measurement displacement system and their respective data acquisition system(s) are coupled to the specified blade using a mechanical, magnetic, or adhesive gripping mechanism. The delivery snake arm is removed and the installed system logs displacement and rotational data as the rotor rotates. To retrieve the data acquisition system the arm is again inserted to deactivate the griping mechanism and retrieve the data acquisition system. Data collected can be either stored the data acquisition system internal storage, removable media, or can be streamed wirelessly in real time during measurement. Data collected can also be communicated via a direct cable connection. A data analyzer coupled to the data acquisition system correlates blade tip and circumscribing turbine casing radial clearance gap relative to rotational position with the displacement and rotational data sets. This method and apparatus provide an accurate and cost effective solution for accessing turbine casing visual condition. With the optional blade tip gap measurement system, case deformation impact on blade tip clearance and rotor/casing alignment can be determined while performing the visual inspection with the camera system. 
       FIGS. 1 and 2  show schematically a gas turbine  20 , with a turbine casing having an inner circumferential ring segment  22  that defines an inner diameter and an access port  23 . Rotor  24  rotates within the turbine  20 . Affixed to the rotor  24  are a plurality of rows of turbine blades  26  that are designated B l -B N . The reference number  26  and its lead line throughout the figures specifically points to the airfoil surface portion of the blade. Only a single blade row is schematically shown in  FIG. 1 . As a blade  26  rotates with the rotor  24 , it defines a rotational displacement θ; its blade tip  28  sweeps the circumscribing inner circumferential ring segment  22 . Radial separation between the mutually opposed and spaced blade tip  28  and the inner diameter of the ring segment  22  is designated by gap g. 
     The blade tip clearance system  30  embodiment shown in  FIGS. 1 and 2  comprises a blade mounted instrument  32  that is communicatively coupled to a blade tip clearance data analyzer system  34 . In this embodiment communication is established via wireless communication system, for example one utilizing Bluetooth communications protocol. The data analyzer system  34  may be incorporated into a personal computer  36 . Details of the blade clearance system  30  architecture and function are further described. 
     The blade mounted instrument  32  includes a displacement probe system  40 , which as shown in  FIGS. 1 and 2  is a non-contact type displacement probe having at least one photonic energy transmitter  42  and a corresponding receiver  44  of known construction.  FIG. 2  shows a probe  40  having an arrayed pair of transmitters and receivers. In this embodiment the transmitted and received photonic energy is in the infra-red spectrum. Alternatively, visible light or ultrasonic non-contact displacement probes or mechanical displacement measurement displacement probes may be substituted for the non-contact probe  40  that is shown in  FIG. 1 . The displacement probe  40  generates a displacement data set of relative distance between the probe and the circumscribing turbine casing circumferential ring  22 . A rotor rotational position acquisition system sensor  60  is also coupled to the blade  26  in order to sense the rotor/corresponding blade&#39;s rotational positionθ and generate a rotational position data set. The rotational position sensor  60  is of known construction, exemplary embodiments of which may include known tilt, gyroscopic or localized triangulated GPS-type sensors. Alternatively the rotational position sensor function may be performed by an existing turbine rotor  24  rotational position sensor  260  as shown in  FIG. 8 . 
     The blade mounted displacement probe system  40  and the rotor/blade rotational system sensor  60  are coupled to data acquisition module  70  that acquires the displacement and rotational position data sets. While the data acquisition module  70  is shown coupled to the turbine blade  26  and receives both the displacement and rotational position data sets, alternative locations and data feed configurations are possible in other embodiments. For example, the sensors  40  and  60  may be coupled jointly or severally to a wireless communication module that in turn communicates with a non-blade mounted data acquisition module. Similarly the data acquisition module function may be divided into separate components that receive separate positional or displacement data sets from the respective sensors  40  and  60 . 
     The data acquisition module  70  sends the displacement and rotational position data sets to the data analyzer system  34  via wireless Bluetooth communication with the data analyzer system interface  80 . The data analyzer system  34  includes the data analyzer interface  80  and the personal computer  36 ; the latter correlates blade tip and circumscribing turbine casing radial clearance gap relative to rotational position with the displacement and rotational data sets received from the data acquisition module  70 . Blade tip gap g information and relative rotational position in the data analyzer system  34  is available for further analysis, including by way of example relative concentric alignment of the rotor, rotor blades, turbine vanes and the turbine casing inner diameter, concentricity of the turbine casing itself and identification of potential localized wear patterns within the turbine casing lining. If multiple displacement probes  40  are utilized across the axial length of the blade tip  28  annular patterns, rather than just circular patterns of blade tip gap g about the turbine casing circumference can be acquired and analyzed. 
     As shown in  FIG. 3  by the double arrow the blade mounted instruments  32  can be installed and removed via a turbine access port  23  or manway, or by removing a section of the turbine external housing that does not circumscribe the blade tips  28 . Similarly, if a wireless communication system is not utilized between the data acquisition module  70  and the data analyzer system  34 , a portable memory device may be incorporated into the data acquisition module and to store the acquired rotational and/or displacement data sets. The memory device is removed after data acquisition by the blade tip clearance system  30  and subsequently transported as shown schematically by the double lines for coupling to the data analyzer interface  80 ′ and for subsequent downloading of the data sets. Alternatively, as shown in  FIG. 4 , the data acquisition module  70  may be communicatively coupled to the data analyzer interface  80 ″ by a physical cable  82  routed through an access port  23 . The cable  82  has sufficient length to be wrapped around the turbine rotor  24 . 
     As previously noted the blade mounted instruments  32  are coupled or otherwise affixed to the blade  26  so that they do not inadvertently drop within the turbine interior during a blade gap measurement procedure. As shown in  FIG. 5 , a probe  40  of the blade mounted instrument is coupled to the blade  26  by a hook and loop fastened strap  50  that is circumferentially wrapped about the blade. In  FIG. 6  the probe  40  is coupled to the blade  26  by a retaining clamp  50 ′, having opposed plates that are compressively coupled to a turbine blade circumference by screws. 
       FIG. 7  shows an alternative embodiment of a blade tip clearance system blade mounted instrument  132  that is advantageously a printed circuit board upon which are mounted a pair of non-contact, infra-red spectrum photonic displacement probes  142  that are oriented on opposite lateral ends of the blade for generation of displacement data sets. Each of the probes  142  has an infra-red transmitter  142  and an infra-red receiver of known construction. Magnets  150  on opposite sides of the blade mounted instrument  132  couple the instrument to the blade  26  in a fixed position. A tilt sensor  160  generates the rotational positional data set. Data acquisition module  170  is coupled to the displacement probes  140  and the tilt sensor  160  for acquiring the displacement and rotational position data sets and communicating them to the previously described data analyzer system  34  via wireless communication or via physical transfer of a data storage device. Battery  180  powers the blade mounted instrument  132 . 
     The blade mounted instrument  232  of  FIGS. 8 and 9  comprise a contact displacement probe  240  with a displaceable probe tip  242  that is in contact with the blade circumscribing turbine casing inner diameter surface  22 . Physical displacement of probe tip  242 , as shown by the double-ended arrow, generates a displacement data set. The blade mounted instrument  232  is coupled to blade  26  by one or more magnets  250 . Displacement data generated by the contact displacement probe  240  is gathered by data acquisition module  270  that in turn routes the displacement data to the data analyzer system interface  280  via wireless communication (e.g., Bluetooth) protocols, as previously described. The turbine blade rotational positional data set is generated by the turbine rotor positional sensor  260  rather than a blade-mounted positional sensor. The rotational positional data set is routed to the data analyzer system  234  by known means, such as a communications cable. The data analyzer system  234  correlates the received displacement and rotational position data sets with blade gap about the turbine casing inner diameter  22  as previously described. 
     In  FIGS. 10 and 11  a blade mounted optical inspection system of the invention includes an optical camera  340  that is coupled to a blade  26  for generating and capturing images within its field of view (FOV) within the turbine  20 . The blade mounted data acquisition system  370  acquires the camera image information and routes it to the data analyzer system interface  380  via wireless communication while the rotor rotational position sensor  360  sends a rotational position data set to the data analyzer system computer  36 . The optical inspection system camera  340  may capture images within a desired spectral bandwidth (e.g., visible, infra-red, etc.) and may be utilized jointly with or separately from a blade gap measurement system. 
     Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The invention is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.