Abstract:
An apparatus and method for remote frequency-based inspection of a valve seat includes inserting a frequency-based inspection tool into an inspection position over the valve seat and contacting the one or more supports to the inner surface of the valve seat. An input signal is transmitted at a desired frequency through the valve seat to a joint between the valve seat and a valve shaft via the one or more transducers. The shaft is rotated to remotely rotate the fixture, thereby allowing an inspection of an entire perimeter of the joint. An output signal is received and is evaluated to determine if an anomaly is present in the joint.

Description:
BACKGROUND 
     The subject invention relates to steam turbines. More particularly, the invention relates to an apparatus and method for inspection of steam turbine valve seats. 
     Steam turbine valve seats are subject to periodic inspection for wear or damage that, if not corrected, would eventually cause significant damage to the steam turbine. In many cases, the valve seat is formed from metal, for example a wear resistant metal such as satellite, and affixed to a steel valve opening. A bond joint between the valve seat and valve opening is inspected to ensure the continued integrity of the joint. The standard inspection method for this joint utilizes penetrants. The penetrant inspection can reveal cracks or other abnormalities in the joint, but only in visible areas, for example an edge, but not in areas of the joint which are not visible. Additionally, because the valve seats are relatively inaccessible for inspection when installed in the steam turbine, the valve seats are inspected in-place in the steam turbine. There is, however, considerable risk of not detecting damage to the valve seat, valve body, or other components because of poor access and visibility of the junction between the stellite inlay and the surrounding steel of the valve seat. Further, penetrant inspection only permits an inspection of the exposed junction between the inlay material and the base material of the valve seat. Disassembly of large valve seats from valve bodies is difficult, expensive and not performed unless the seat is to be replaced with a new seat. 
     Frequency-based inspection, for example, ultrasonic inspection, is another possible method of inspection for valve seats. It permits the inspection of the interface between the stellite inlay and the steel of the valve seat. So it extends the inspection region to include the region that the penetrant examination cannot test. In frequency-based inspection, a probe containing one or more transducers connected to a diagnostic machine is passed over the object being tested. The transducer sends pulsewaves into the surface of the object, and an output signal is received by a receiver. The screen on the diagnostic machine will show these results in the form of amplitude and pulse readings, as well as the time it takes for the waves to reach the receiver. This data is evaluated to determine if an anomoly is present. 
     Frequency based inspection has not been utilized to inspect installed valve seats because of lack of access and the difficulty of accessing the stellite inlay from the end of a large valve, and/or line of sight visibility to the valve seat surface when installed. Without physical access for large valves and/or line of sight visibility, there may be noise signals present in the inspection data generated by, for example, variable lift-off of the probe from the valve seat surface and/or wobble of the probe on the valve seat surface. These noise signals may prevent accurate inspection results. Removing the valve seats for inspection presents the same risks of damage and increase in inspection time as noted above for penetrant inspection. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A remote frequency-based inspection tool for a valve seat comprises a fixture receivable in a valve seat, and a shaft fixed to the fixture allowing remote manipulation of the fixture. The fixture includes one or more transducers contactable with an inner surface of the valve seat when the fixture is in an inspection position and one or more supports contactable with the inner surface of the valve seat when the fixture is in an inspection position. 
     A method of remote frequency-based inspection of a valve seat comprises inserting the inspection tool into an inspection position over the valve seat and contacting the one or more supports to the inner surface of the valve seat. An input signal is transmitted at a desired frequency through the valve seat to a joint between the valve seat and a valve shaft via the one or more transducers. The shaft is rotated to remotely rotate the fixture, thereby allowing an inspection of an entire perimeter of the joint. An output signal is received and is evaluated to determine if an anomaly is present in the joint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of an embodiment of a frequency-based inspection tool for a valve seat; 
         FIG. 2  is a section view of the fixture portion of the tool of  FIG. 1 ; 
         FIG. 3  is a detail view of an embodiment of a fixture illustrating an exemplary transducer configuration; 
         FIG. 4  is a plan view of an embodiment of a fixture; and 
         FIG. 5  is a partial plan view of an embodiment of a shaft and a stabilizer. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION 
     A device  10  for frequency-based inspection of a valve seat  12  in, for example, a steam turbine, is shown in  FIG. 1 . In one embodiment, the device  10  includes a fixture  14  configured to be receptive in the valve seat  12 . As shown in  FIG. 2 , the fixture  14  includes an outer surface  16  that substantially conforms to an inner surface  18  of the valve seat  12 . The shape of the fixture  14  may be configured to conform to many types of valve seats  12  including, for example, a stop valve seat or control valve seat. The fixture  14  includes one or more ports  20  that are receivable of one or more transducers  22 . As shown in  FIG. 3 , in one embodiment, the transducers  22  are disposed in a transducer carrier  24 . The transducers  22  are disposed within the fixture  14  such that when the fixture is positioned at the valve seat  12  to be inspected, the transducers  22  are substantially facing the surface  18 . In some embodiments, the transducers  22  may be spring loaded, allowing the transducers  22  to project toward surface  18 , and stops  26  may additionally be included in the ports  20  to limit travel of the transducers  22 . The embodiment shown in  FIG. 4  includes  3  transducers ports  20  arranged substantially equally spaced around the perimeter of the fixture  14 . This configuration provides for an accurate and repeatable inspection of the valve seat  12 . It is to be appreciated, however, that other quantities and arrangements of transducer ports  20  and transducers  22  are contemplated within the scope of this invention. In some embodiments, the transducers  22  operate at frequencies greater than 50 kilohertz, or ultrasonic frequencies. Further, in one embodiment, the transducers  22  operate at a frequency of about 5 megahertz. Utilizing 5 megahertz transducers  22  provides the resolution and sensitivity necessary to reveal small cracks and/or imperfections in the valve seat  12 . It is to be appreciated, however, that other transducer  22  frequencies are contemplated within the scope of this invention. 
     As shown in  FIG. 4 , the fixture  14  includes one or more supports  28  to support the fixture  14  in the valve seat  12 . Supporting the fixture  14  in the valve seat  12  helps ensure accuracy of the inspection by preventing unwanted movement of the fixture  14  during the inspection process, thus minimizing noise signals. In one embodiment, the supports  28  are roller bearings  30 , but other means may be utilized as supports  28 . Referring now to  FIG. 2 , each roller bearing  30  is held by a bearing support  32 , which is disposed in a bearing hole  34  in the fixture  14 . The roller bearings  30  are located equally spaced around the perimeter of the fixture  14 , and are located substantially equidistant between transducer ports  20 . In a fixture  14  shown in  FIG. 4  where three transducers ports  20  are utilized, three supports  28  are employed, but other quantities of supports  28  are contemplated within the scope of this invention. Referring again to  FIG. 2 , the roller bearings  30  are configured and disposed such that when the fixture  14  is moved into an inspection position at the valve seat  12 , the roller bearings  30  contact surface  18  of the valve seat  12 , thus providing support for the fixture  14  while allowing the fixture  14  to be easily rotated for scanning inspection of the valve seat  12 . 
     Referring now to  FIG. 1 , the fixture  14  is fixed to a shaft  34 , such that the shaft  34  extends from the fixture  14  substantially perpendicular to a measurement face  36 . For example, the shaft  34  may be inserted into and retained in a shaft hole  38  disposed in the fixture  14 . In some embodiments, one or more stabilizers  40  may be disposed along the shaft  34 . The stabilizers  40  include one or more support arms  42  extending radially outward to support the shaft  34  and prevent unwanted movement of the shaft  34  and the attached fixture  14  during inspection of the valve seat  12 . In some embodiments, the support arms  42  include a strongly magnetic plate  44  which, when contacted with the steam turbine structure, further stabilizes the shaft  34  and fixture  14  by further preventing unintended movement of the shaft  34  and fixture  14 . This may be especially useful in inspecting valve seats  12  that lie substantially in a vertical plane such that the shaft  34  is substantially horizontal during the inspection, such as a stop valve seat, for example. As illustrated in  FIG. 5 , in some embodiments, a retention bushing  46  and a clamp ring  48  are employed to retain the stabilizer  40  in an axial position on the shaft  34 . The retention bushing  46  is installed and retained on the shaft  34  by, for example, press fit. The stabilizer  40  is installed on the shaft  34  and rests on the retention bushing  46 . To retain the stabilizer  40  in its desired position on the shaft  34 , the clamp ring  48  in installed on the shaft over the stabilizer  40 . A clamp ring screw  50  is the tightened, thus retaining the clamp ring  48  on the shaft  34 . One or more springs  52  may be disposed between the clamp ring  48  and the stabilizer  40 , and/or between the stabilizer  40  and the retention bushing  46  to allow some flexibility in the axial position of the stabilizer  40  on the shaft  34 . 
     Referring again to  FIG. 1 , some embodiments of the inspection device  10  may include a scanning control ring  54 . The scanning control ring  54  is fixed to the shaft  34  at an end opposite to the fixture  14 . The scanning control ring  54  allows an inspection operator to control rotation of the fixture  14  to perform inspection of the valve seat  12 . 
     To perform an inspection of a valve seat  12 , the device  10  is inserted into the steam turbine, and the fixture  14  is positioned over the valve seat  12  to be inspected. The supports  28  contact surface  18  on the valve seat  12 , and the transducers  22  are positioned over surface  18 . The supports  28  and the stabilizer  40  prevent undesired motion or lift-off of the fixture  14  relative to the valve seat  12 , preventing noise signals from the transducers  22  thus resulting in a more accurate inspection of the valve seat  12 . Referring now to  FIG. 2 , the transducers  22  transmit input signals through the valve seat  12  and a signal is received by a receiver. In the embodiment shown in  FIG. 2 , the transducers  22  are configured such that the output signal is reflected to the transducer  22  if an anomaly is encountered, indicating a flaw in a joint  56  between the valve seat  12  and a valve shaft  58 . The inspection operator rotates the fixture  14  by turning the scanning control ring  54  to inspect the entire surface  18  of the valve seat  12 . 
     The device  10  can be either manually or automatically driven. With encoders attached, a transducer  22  position along surface  18  can be determined and used with the received signals to provide a computer display of indications or anomalies in the valve seat  12  and the joint  56 . This permits the presentation of the signals as an image or table for evaluation of the quality of the joint  56  and also of the valve seat  12 . Various levels of data capture, recording, analysis and evaluation from using either written records or proceeding to a fully computerized inspection system are possible. The preferred implementation is to use a skilled operator with a manual inspection. 
     While embodiments of the invention have been described above, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.