Abstract:
A system for online monitoring the condition of a thermal barrier coating on the vanes and/or blades of a combustion turbine, or other forms of component deterioration affecting the acoustic properties of the vanes and/or blades. The system begins with a signal generator for transmitting a signal to an acoustic transmitter, and then to an acoustic waveguide secured within the turbine, adjacent to a vane. Acoustic waves passing through the vane&#39;s coating will have a certain magnitude and velocity when passing through an intact coating, which will change as the coating deteriorates. Additional variation of the acoustic wave will occur due to pressure pulses from passing blades, with the magnitude of the pressure pulses increasing as the blade&#39;s coating deteriorates. The acoustic waves are then received by a second acoustic waveguide. The resulting signal will be converted from an acoustic signal to an electrical signal by an acoustic receiver, and will pass through a filter to remove the lower frequency signals of the turbine from the higher frequency signals to be analyzed. The remaining higher frequency signals are sent to a computer, permitting the variations in the acoustic waves to be analyzed. A second embodiment relies solely on pressure pulses from passing blades to generate acoustic signals within the vanes.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to online monitoring of combustion turbines for defects. More specifically, the invention is an apparatus and method for using acoustic signals to monitor the condition of combustion turbine component online.  
           [0003]    2. Background Information  
           [0004]    Combustion turbines typically operate at extremely high temperatures, for example, 2500° F. to 2900° F. (1371° C. to 1593° C.). Such high temperatures will cause failure of various components unless they are protected from the heat. These components include the rotating blades of the turbine, and the vanes for directing gas flow within the turbine. A typical combustion turbine will have three to four rows each of blades and vanes, with approximately 50 to 100 blades or vanes per row, and will typically have approximately 500 total blades and vanes to protect. A commonly used material for vanes and blades is nickel-cobalt. These components are usually insulated by a thermal barrier coating to enable their use within high temperature environments. A typical thermal barrier coating is yttria-zirconia.  
           [0005]    Currently, it is necessary to periodically stop the turbine and inspect the components for deterioration of the thermal barrier coating, defects in other coatings, or other defects, for example, formation of cracks. It would be desirable to monitor the condition of these components while the turbine is in use. Avoiding the need to periodically stop the turbine for inspection reduces downtime, increasing the turbine&#39;s efficiency. Similarly, early detection of defects reduces repair costs and outage time, again increasing turbine efficiency. A need exists for providing earlier detection of defects, and a means of locating the defect, simplifying the inspection and repair procedure once a defect is identified.  
           [0006]    One proposed system for detecting and locating defects within turbine components is described in U.S. Pat. No. 5,445,027 issued to W. Zörner on Aug. 29, 1995. The system involves using a probe on the housing of the turbine to measure the acoustic spectrum of the turbine. This acoustic spectrum is then compared with a reference spectrum, with deviations from this reference spectrum indicating a damaged turbine blade. A preferred embodiment of this method includes generating an acoustic signal to increase the intensity of the acoustic spectrum within the turbine.  
           [0007]    U.S. Pat. No. 5,942,690 issued to A. Shvetsky on Aug. 24, 1999, describes an apparatus and method for ultrasonic inspection of rotating machinery while the machinery is in operation. The method uses an ultrasonic transducer to radiate pulses of ultrasonic energy at a frequency substantially equal to a subharmonic of the frequency of the turbine rotation. The transducer will sense reflections of the ultrasonic pulses from the blade, and convert the reflections into an electrical signal. Changes in the reflected signal can indicate a damaged blade. If this apparatus and method were used with a combustion turbine, it would be difficult to precisely direct an acoustic wave through the high pressure, flowing gas present within the turbine.  
           [0008]    Accordingly, there is a need to provide an online monitor for identifying the onset of a change in the condition of combustion turbine components. Additionally, there is a need identify the general location of the defect. Further, there is a need to detect the inception of defects within a coating protecting these components.  
         SUMMARY OF THE INVENTION  
         [0009]    The invention is a system for monitoring the condition of a component within a combustion turbine during operation of the turbine, and in its preferred form can be used to monitor the thermal barrier coating on the blades and vanes within the turbine. The system relies on detecting changes in the magnitude and/or velocity of acoustic waves created by gas pressure exerted on the vanes (for directing gas flow) and blades (for converting the gas pressure into work).  
           [0010]    As the combustion turbine is operated, a pulse signal generator will generate a signal to an acoustic transmitter, which will convert the electrical signal to an acoustic wave for transmittal through a high frequency acoustic waveguide to each vane. Acoustic waves passing through each vane are received by a second acoustic waveguide. An acoustic waveguide receiver will transmit a signal corresponding to the acoustic waves received to an acoustic receiver for conversion of the acoustic signal to an electrical signal. The signal is then transmitted to a filter to remove the lower frequency signals of the turbine from the higher frequency signals to be analyzed. The signal is finally sent to a storage scope and/or computer, permitting the variations in the acoustic waves to be analyzed.  
           [0011]    If only monitoring the condition of the vanes, a pulsed acoustic signal may be sent through the vanes. The resulting acoustic wave will have a certain magnitude and velocity when passing through a vane with an intact coating. The magnitude and velocity of the acoustic wave will vary according to the condition and bond strength of the thermal barrier coating, and the strain to which the vane is subjected. As the coating on the vane deteriorates, the magnitude and/or velocity of the resulting acoustic wave will change, indicating that a vane needs servicing.  
           [0012]    A rapid sequence of pulses, approximating a steady acoustic wave, or a continuous sine wave, may be generated to measure coating wear on both the blades and the vanes. A rapid sequence of pulses ensures that a pulse is present as a blade passes the vane. The measured magnitude of the acoustic waves at one vane will increase as a blade passes that vane due to the gas pressure, which will produce a regular pattern of increasing and decreasing magnitude in the acoustic waves as long as all blades are in good condition. As before, the magnitude and velocity of the acoustic wave will vary according to the condition and bond strength of the thermal barrier coating, and the strain to which the blade is subjected. As the coating on the blades deteriorates, the magnitude and/or velocity of the resulting acoustic wave will change, indicating that a blade needs servicing.  
           [0013]    Alternatively, acoustic signals within the turbine can be monitored without the need for generating the acoustic signal. As each blade passes a vane, the blade will produce a gas pressure pulse and resulting acoustic wave at that vane. The acoustic waves are received by an acoustic waveguide. The acoustic waveguide will transmit the acoustic wave to an acoustic receiver for converting the acoustic signal to an electrical signal. The electrical signal will then be transmitted to a filter to remove the lower frequency signals of the turbine from the higher frequency signals to be analyzed. The signal is finally sent to a storage scope and computer, permitting the variations in the acoustic waves to be analyzed. A particular acoustic signal having increasing magnitude indicates a blade having a deteriorating coating.  
           [0014]    It is therefore an aspect of the present invention to provide an apparatus for monitoring the condition of a component within a turbine while the turbine is operating.  
           [0015]    It is another aspect of the present invention to provide an apparatus for monitoring the condition of a coating on a component within a turbine while the turbine is operating.  
           [0016]    It is therefore a further aspect of the present invention to provide an apparatus for monitoring the condition of a thermal barrier coating on the components of a combustion turbine while the turbine is operating.  
           [0017]    It is another aspect of the present invention to provide a method for monitoring the condition of a thermal barrier coating on the components of a combustion turbine while the turbine is operating.  
           [0018]    It is a further aspect of the present invention to determine the status of a thermal barrier coating by passing an acoustic wave through that coating, and analyzing the acoustic wave for changes in magnitude.  
           [0019]    A better understanding of the present invention can be obtained from the following description, with reference to the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a cross sectional view of a combustion turbine for which the present invention will be used.  
         [0021]    [0021]FIG. 2 is a cross sectional view of the turbine portion of a combustion turbine, illustrating the placement of the acoustic waveguides within the turbine, according to the present invention.  
         [0022]    [0022]FIG. 3 is a schematic diagram of a pulse signal generator used according to the present invention.  
         [0023]    [0023]FIG. 4 is a schematic diagram of the turbine portion of a combustion turbine, illustrating the placement of the acoustic waveguides within the turbine, according to the present invention.  
         [0024]    [0024]FIG. 5 is a schematic diagram of the apparatus used to store and analyze acoustic signals according to the present invention, including a filter, a storage scope, a computer, a spectrum analyzer, an acoustic emission counter, and a printer.  
         [0025]    [0025]FIG. 6 is a schematic diagram of an acoustic signal pattern resulting from a pulsed signal, indicating an uncoated vane.  
         [0026]    [0026]FIG. 7 is a schematic diagram of an acoustic signal pattern resulting from a pulsed signal, indicating an intact coating on a vane.  
         [0027]    [0027]FIG. 8 is a schematic diagram of an acoustic signal pattern resulting from a pulsed signal, indicating a deteriorating coating on a vane.  
         [0028]    [0028]FIG. 9 is a schematic diagram of an acoustic signal pattern resulting from a constant signal, indicating an intact coating on a vane and on the blades passing the vane.  
         [0029]    [0029]FIG. 10 is a schematic diagram of an acoustic signal pattern resulting from a constant signal, indicating an intact coating on a vane and a deteriorating coating on one blade passing the vane.  
         [0030]    [0030]FIG. 11 is a schematic diagram of an acoustic signal pattern resulting from a constant signal, indicating a deteriorating coating on a vane and an intact coating on one blade passing the vane.  
         [0031]    [0031]FIG. 12 is a schematic diagram of an acoustic signal pattern resulting from a series of pressure pulses applied to intact thermal barrier coatings.  
         [0032]    [0032]FIG. 13 is a schematic diagram of an acoustic signal pattern resulting from a series of pressure pulses applied to a vane having an intact coating by a blade having a deteriorating coating.  
         [0033]    [0033]FIG. 14 is a schematic diagram of an acoustic signal pattern resulting from a series of pressure pulses applied to a vane having a deteriorating coating by a blade having an intact coating.  
         [0034]    Like reference numerals denote like elements throughout the drawings. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    The preferred embodiment of the invention is a system for online monitoring the condition of the vanes and blades within a combustion turbine. The system permits monitoring any condition resulting in changes to the acoustic properties of components within the combustion turbine, such as deterioration of the thermal barrier coating covering the blades and vanes. The significance and functioning of the present invention are best understood through a description of the environment within a combustion turbine.  
         [0036]    [0036]FIG. 1 illustrates a combustion turbine  10 . The combustion turbine  10  includes a compressor  12 , at least one combustor  14 , and a turbine  16 . The turbine  16  includes a plurality of rotating blades  18 , secured to a rotatable central shaft  20 . A plurality of stationary vanes  22  are positioned between the blades  18 , with the vanes  22  being dimensioned and configured to guide air over the blades  18 . The blades  18  and vanes will typically be made from nickel-cobalt, and will typically be coated with a thermal barrier coating  26 , such as yttria-zirconia.  
         [0037]    In use, air is drawn in through the compressor  12 , where it is compressed and driven towards the combustor  14 . The combustor  14  mixes the air with fuel and ignites it, thereby forming a working gas. This working gas will typically be approximately 2500° F. to 2900° F. (1371° C. to 1593° C.). This gas expands through the turbine  16 , being guided across the blades  18  by the vanes  22 . As the gas passes through the turbine  16 , it rotates the blades  18  and shaft  20 , thereby transmitting usable mechanical work through the shaft  20 . The combustion turbine  10  also includes a cooling system  24 , dimensioned and configured to supply a coolant, for example steam or compressed air, to the blades  18  and vanes  22 .  
         [0038]    From the above description, it becomes apparent that the environment wherein the vanes  22  and blades  24  operate is particularly harsh, resulting in serious deterioration of the blades  18  and vanes  22  if the thermal barrier coating  26  should deteriorate. Further, such an environment is likely to cause other forms of component deterioration, such as deterioration of coatings for corrosion prevention, or formation of cracks within the coatings, or the underlying components. Although the description below relies on the example of monitoring of thermal barrier coating deterioration within a combustion turbine, the same procedure may be used for online monitoring of any form of deterioration affecting the acoustic characteristics of the turbine, or possibly thermal barrier coatings used for other applications wherein pressure, stress, and/or friction are applied to the coated component.  
         [0039]    Although the monitoring system described herein will preferably be used with every vane  22  for which monitoring is desired within the turbine  16 , which may be all vanes or only those vanes subjected to the highest temperatures and pressures, the system will be described herein using only a single vane  22 . Referring to FIGS. 2 and 4, means for generating and receiving acoustic signals within the coating  26  (or within a component if other forms of deterioration are measured), which are preferably a pair of acoustic waveguides  28 , 30 , are illustrated proximate to, and preferably secured to, a vane  22 . A special feature of acoustic waveguides is that they can be bonded to vanes by either a point or direct contact or by bonding a few inches of acoustic waveguide length to the vane edges. In this way, either longitudinal waves or slow-moving surface waves can travel through the vane for interrogation. Referring to FIGS.  3 - 4 , acoustic waveguide  28  is attached to an acoustic transmitter  58 , which is attached to a pulse signal generator  32  by electrical lead  31 . Referring to FIG. 5, acoustic waveguide  30  is attached to an acoustic receiver  60 , which is attached to a filter  34  by electrical lead  33 . A preferred filter is a high pass filter removing acoustic waves below 30 kHz. The filter  34  is attached to means for analyzing the acoustic signal to determine the existence and location of a defect within the coating. These components preferably include a storage scope  36  for measuring and storing information about the magnitude and velocity of the acoustic waves, computer  38  for analyzing the stored data, preferably using pattern recognition software, spectrum analyzer  40  for observing changes in the magnitude of acoustic waves at frequencies other than those generated by acoustic waveguide  28 , acoustic emission counter  42  for detecting additional noise within the combustion turbine, as would be generated by a component approaching failure, and/or printer  44  for printing various collected data. Once the information is collected and stored, it may be analyzed as described below.  
         [0040]    Depending on the type of monitoring desired, the pulse signal generator  32  may generate either a pulsed or a steady acoustic signal. Pulsed signals are useful for monitoring the coating  26  on the vanes  22 . More rapidly pulsed signals, approximating a steady stream of pulses, are useful for monitoring the coating on the vanes  22  and blades  18 . A sufficiently rapid, constant flow of pulses, preferably approximating a steady signal, ensures that a pulse will be present as a blade  18  passes the vane  22 , permitting reliable monitoring of both the vane  22  and blades  18 . A preferred and suggested acoustic wave will be 70 to 80 kHz., transmitted at 150 pulses per second in bursts of 32 Hz. Such an acoustic wave will permit monitoring of both blades and vanes.  
         [0041]    To monitor the vanes during operation of the turbine, pulse signal generator  32  will generate a pulsed signal. The pulsed signal is transmitted to the acoustic transmitter  58 , which is bonded to the acoustic waveguide  28 , and may be a piezoceramic crystal, preferably resonant in the 70-80 kHz region. Acoustic waves from the acoustic transmitter  58  then travel through the acoustic waveguide  28 , to the coating  26  of vane  22  as a high frequency acoustic wave. The acoustic wave travels through the coating  26  of the vane  22 , before being received by the acoustic waveguide  30 . The acoustic waveguide  30  will of course receive any acoustic waves within the turbine  16 , in addition to the desired acoustic signals. The acoustic waveguide  30  then transmits the received acoustic waves to the acoustic receiver  60 , which is preferably a piezoelectric crystal resonant in the 70-80 kHz region, converting the acoustic waves back to electrical pulses. This signal then passes through a filter  34  for removal of the low frequency acoustic signals generated through normal operation of the combustion turbine, leaving only the high frequency acoustic signal generated for interrogating the coating  26 . The signal can then be measured and stored by the storage scope  36 , analyzed using the computer  38 , processed by the spectrum analyzer  40  and acoustic emission counter  42  to locate any other acoustic irregularities, and possibly printed using printer  44 .  
         [0042]    Using the above-described procedure, an acoustic wave passing through an uncoated vane is illustrated in FIG. 6, as sinusoidal display  46   a . An acoustic wave passing through an intact coating  26  will have a significantly lower magnitude, as illustrated in FIG. 7, as sinusoidal display  46   b  having peaks  50 . An acoustic wave passing through a partially deteriorated coating  26  will have a magnitude between that of sinusoidal display  46   a  and  46   b , such as sinusoidal display  46   c  illustrated in FIG. 8. Therefore, increasing magnitude of the sinusoidal display indicates an increasing magnitude of the represented acoustic signal, indicating a deteriorating thermal barrier coating  26 . In addition, it is anticipated that the wave velocity for an intact coating will be low, around 2500 m/sec, and will increase as the coating deteriorates to near 5,000 m/sec once the coating has totally deteriorated. The velocity is calculated from the time required for the acoustic wave to travel through the coating.  
         [0043]    Alternatively, both blades  18  and vanes  22  may be monitored by using a constant acoustic wave. Pulse generator  32  generates a steady electronic signal, which is then converted to an acoustic wave by the acoustic transmitter  58 , and transmitted by the acoustic waveguide  28  as a high frequency acoustic wave through the coating  26  of a vane  22 . The acoustic waveguide  30  will receive the acoustic signal transmitted through coating  28 , and will also receive another acoustic signal having a wide range of frequencies, created within the coating  26  of the vane  22  when a blade  18  passes the vane  22 . The acoustic waveguide  30  will of course receive any acoustic waves within the turbine  16 , in addition to the desired acoustic signals. The acoustic waveguide  30  then transmits the received signal to an acoustic receiver for converting the acoustic wave to an electronic signal. The electronic signal is then passed through a filter  34  for removal of the low frequency acoustic signals generated through normal operation of the combustion turbine, leaving only the high frequency acoustic signal generated by acoustic waveguide  28 , and the high frequency portion of the acoustic signal from the pressure pulse of the blade  18  passing the vane  22 . The signal can then be measured and stored by the storage scope  36 , analyzed using the computer  38 , processed by the spectrum analyzer  40  and acoustic emission counter  42  to locate any other acoustic irregularities, and possibly printed using printer  44 .  
         [0044]    FIGS.  9 - 11  illustrate simulated sinusoidal displays  48   a , 48   b , 48   c  resulting from the above-described procedure. As illustrated in FIG. 9, the sinusoidal display  48   a  includes a series of smaller peaks  50 , resulting from acoustic signals generated by the acoustic waveguide  28  only through the coating  26  of the vane  22 . The peaks  50  in FIGS.  9 - 11  are therefore representative of the same acoustic signal (the acoustic wave passing through the vane without a pressure pulse from a blade) as the peaks  50  of FIGS.  6 - 8 , with the only difference being that FIGS.  9 - 11  depict a constant stream of acoustic signals while FIGS.  6 - 8  illustrate individual acoustic signals having larger time intervals separating them from other signals. As the coating  26  of a vane deteriorates, the magnitude of the peaks  50  will increase in the same manner illustrated in FIGS.  6 - 8  and described above. The sinusoidal displays  48   a , 48   b  also include larger peaks  52   a , 52   b , created by the pressure pulse created by a blade  18  passing a vane  22 . FIG. 9 illustrates a sinusoidal display  48   a , wherein all blades  18  and vanes  22  have intact coatings  26 , and therefore all peaks  52   a  are the same height. FIG. 10 illustrates a sinusoidal display  48   b , wherein all vanes  22  have intact coatings  26 , but one blade  18  has a deteriorating coating  26 , resulting in the peaks  52   b  having a larger magnitude than the peaks  52   a . Such a situation should result in a sinusoidal display  48   b  for all vanes  22  associated with the blade  18  having the deteriorating coating  26 , because that blade  18  will generate the same pressure pulse while passing all such vanes  22 . FIG. 11 illustrates a sinusoidal display  48   c , wherein the vane  22  to which the acoustic waveguides  28 , 30  in question are attached has a deteriorating coating  26 , but all blades  18  have an intact coating  26 , resulting in an increase in the magnitude of both peaks  50  and  52   a . In such a case, examination of the sinusoidal displays associated with the other vanes  22  should resemble sinusoidal display  48   a  of FIG. 9, assuming that no other blade  18  or vane  22  has a deteriorating coating. It therefore becomes helpful to compare the various acoustic waves generated from a plurality of vanes  22  to more accurately locate a defect.  
         [0045]    As a second alternative, the pulse generator  32  and acoustic waveguide  28  may be omitted, relying completely on the pressure pulse of a blade  18  passing a vane  22  to generate acoustic waves within the coating  26 . The acoustic waveguide  30  will receive these acoustic signals, which will include a broad range of frequencies. The acoustic waveguide  30  will of course receive any acoustic waves within the turbine  16 , in addition to the desired acoustic signals. The acoustic waveguide  30  then transmits the received signal through a filter  34  for removal of the low frequency acoustic signals generated through normal operation of the combustion turbine, leaving only those signals from the pressure pulse of the blade  18  passing the vane  22  that have frequencies exceeding the frequencies of the background noise. The signal can then be measured and stored by the storage scope  36 , analyzed using the computer  38 , processed by the spectrum analyzer  40  and acoustic emission counter  42  to locate any other acoustic irregularities, and possibly printed using printer  44 .  
         [0046]    FIGS.  12 - 14  illustrate sinusoidal displays  54   a , 54   b , 54   c  representing the acoustic waves generated by the above-described pressure pulses. The peaks  56   a  increase in magnitude as a blade  18  passes the vane  22  to which the acoustic waveguide  30  is attached, then gradually decrease in magnitude as the vibrations dampen until the next blade  18  approaches the vane  22 . The coating  26  will damp acoustic waves, so increasing magnitude of peaks indicates a deteriorating coating  26 . FIG. 12 shows a sinusoidal display  54   a  indicating an intact coating on the vane  22  and all blades  18  passing the vane  22 . Each pressure pulse creates a relatively low-magnitude, consistent peak  56   a . FIG. 13 illustrates a sinusoidal display  54   b , indicating that one blade  18  has a deteriorating coating  26 . Most peaks  56   a  are consistent, but the peak  56   b  shows an increase in magnitude. Such a situation should result in a sinusoidal display  54   b  for all vanes  22  associated with the blade  18  having the deteriorating coating  26 , because that blade  18  will generate the same pressure pulse while passing all such vanes  22 . FIG. 14 illustrates a sinusoidal display indicating that the coating  26  of the vane  22  to which the acoustic waveguide  30  is attached is deteriorating. As the blades  18  pass this vane  22 , all peaks  56   b  have increased magnitude. In such a case, examination of the sinusoidal displays associated with the other vanes  22  should resemble sinusoidal display  54   a  of FIG. 12, assuming that no other blade  18  or vane  22  has a deteriorating coating. It therefore becomes helpful to compare the various acoustic waves generated from a plurality of vanes  22  to more accurately locate a defect.  
         [0047]    From the above description, it becomes apparent that, because there are many possible patterns of coating deterioration that may take place within a combustion turbine, there are many possible acoustic waves and resulting sinusoidal displays resulting from the monitoring system of the present invention. Each deteriorating component will influence the sinusoidal display as described above, and the combination of effects can be analyzed to determine which components need service. In the event that the resulting sinusoidal display proves difficult to analyze, the mere fact that there was a change of magnitude in the acoustic waves indicates that the turbine components require inspection and/or service.  
         [0048]    While a specific embodiment of the invention has been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.