Patent Application
20090142194
This present application relates generally to methods and systems for determining turbine blade deformation. More specifically, but not by way of limitation, the present application relates to methods and systems for measuring turbine blade deformation while the turbine is operating.
The turbine blades of industrial gas turbines and aircraft engines operate in a high temperature environment, where the temperatures regularly reach between 600° C. and 1500° C. Moreover, the general trend is to increase the turbine operating temperatures to increase output and engine efficiencies. Thermal stresses placed on the turbine blades associated with these conditions are severe.
In general, turbine blades undergo high level of mechanical stress due to the forces applied via the rotational speed of the turbine. These stresses have been driven to even higher levels in an effort to accommodate turbine blade design that include higher annulus areas that yield higher output torque during operation. In addition, the desire to design turbine blade tip shrouds of greater surface area has added addition weight to the end of the turbine blade, which has further increased the mechanical stresses applied to the blades during operation. When these mechanical stresses are coupled with the severe thermal stresses, the result is that turbine blades operate at or close to the design limits of the material. Under such conditions, turbine blades generally undergo a slow deformation, which is often referred to as “metal creep.” Metal creep refers to a condition wherein a metal part slowly changes shape from prolonged exposure to stress and high temperatures. Turbine blades may deform in the radial or axial direction.
Similarly, compressor blades undergo a high level of mechanical stress due to the forces applied via the rotational speed of the compressor. As a result compressor blades also may undergo the slow deformation associated with metal creep.
As a result, the turbine blade and compressor blade failure mode of primary concern in a turbine is metal creep, and particularly radial metal creep (i.e., elongation of the turbine or compressor blade). If left unattended, metal creep eventual may cause the turbine or compressor blade to rupture, which may cause extreme damage to the turbine unit and lead to significant repair downtime. In general, conventional methods for monitoring metal creep include either: (1) attempting to predict the accumulated creep elongation of the blades as a function of time through the use of analytical tools such as finite element analysis programs, which calculate the creep strain from algorithms based on creep strain tests conducted in a laboratory on isothermal creep test bars; or (2) visual inspections and/or hand measurements conducted during the downtime of the unit. However, the predictive analytical tools often are inaccurate. And, the visual inspections and/or hand measurements are labor intensive, costly, and, often, also yield inaccurate results.
In any case, inaccurate predictions as to the health of the turbine or compressor blade, whether made by using analytical tools, visual inspection or hand measurements, may be costly. On the one hand, inaccurate predictions may allow the blades to operate beyond their useful operating life and lead to a blade failure, which may cause severe damage to the turbine unit and repair downtime. On the other hand, inaccurate predictions may decommission a turbine or compressor blade too early (i.e., before its useful operating life is complete), which results in inefficiency. Accordingly, the ability to accurately monitor the metal creep deformation of turbine and/or compressor blades may increase the overall efficiency of the turbine engine unit. Such monitoring may maximize the service life of the blades while avoiding the risk of blade failure. In addition, if such monitoring could be done without the expense of time-consuming and labor-intensive visual inspections or hand measurements, further efficiencies would be realized. Thus, there is a need for improved systems for monitoring or measuring the metal creep deformation of turbine and compressor blades.
The present application thus describes a tip shrouded turbine blade that may include a target pad disposed on an outer radial surface of the tip shroud, the target pad including a raised surface that protrudes radially outward from the outer face of the tip shroud. The target pad may be substantially cylindrical in shape such that an outer radial face of the target pad is substantially circular in shape. The size of the surface area of the outer radial face of the target pad may be configured to be substantially the same size as an area of measurement for a conventional proximity sensor.
The tip shrouded turbine blade further may include a seal rail. The seal rail may include a fin that projects radially outward from the outer surface of the tip shroud. The radial height of the target pad may be less than the radial height of the seal rail. In some embodiments, the target pad is separate from the seal rail. In other embodiments, the target pad is part of the seal rail.
The present application further describe a set of tip shrouded turbine blades wherein: 1) each tip shrouded turbine blade may include a target pad disposed on an outer radial surface of the tip shroud; 2) the target pad may include a raised surface that protrudes radially outward from the outer face of the tip shroud; and 3) the surface profile of the target pad for each of the tip shrouded turbine blades may be configured to be distinguishable from the surface profile of the target pads for the other tip shrouded turbine blades in the set.
The present application further describe a blade for use in a turbine, the blade including a target pad disposed on an outer radial surface of the blade, wherein the target pad may include a raised surface that protrudes radially outward from the outer radial surface of the blade. The target pad may be substantially cylindrical in shape such that an outer radial face of the target pad is substantially circular in shape.
The present application further describe a system for determining the radial deformation of a tip shrouded turbine blade wherein the system may include: 1) one or more proximity sensors disposed around the circumference of a stage of blades, wherein the one or more proximity sensors take at least an initial measurement and a second measurement of the blade; 2) a control system that receives measurement data from the proximity sensors; and 3) a target pad disposed on the outward radial face of the tip shroud. The control system may be configured to determine a radial deformation of the blade by comparing the initial measurement to the second measurement. The initial measurement and second measurement each may indicate the distance from a tip of the blade to the one or more proximity sensors. The initial measurement and the second measurement may be taken while the turbine is operating.
In some embodiments, the number of the proximity sensors may include two or more proximity sensors. In such embodiments, the control system may determine a rotor displacement from the measurements taken by the two or more proximity sensors, and he control system may account for the rotor displacement when making the determination of the radial deformation of the blade.
In other embodiments, the number of the proximity sensors may include one proximity sensor the control system measures a rotor displacement with one or more rotor probes; and 2) the control system accounts for the rotor displacement when making the determination of the radial deformation of the blade.
The target pad may include a raised surface that protrudes radially outward from the outer face of the tip shroud. The target pad may be substantially cylindrical in shape such that an outer radial face of the target pad is substantially circular in shape. The size of the surface area of the outer radial face of the target pad may be configured to be substantially the same size as an area of measurement for a conventional proximity sensor.
The system may further include a seal rail that includes a fin projecting radially outward from the outer surface of the tip shroud. The radial height of the target pad may be less than the radial height of the seal rail. In some embodiments, the target pad may be separate from the seal rail. In other embodiments, the target pad may be part of the seal rail.
A technique has been developed to measure accurately, reliable, and at a relatively low cost the deformation of turbine blades in real time, i.e., as the gas turbine is operating. Referring now to
As illustrated in
Through conventional means the sensors may be connected to a control system (not shown), which may receive, store and make calculations based on the proximity data acquired by the proximity sensors 22. The control system may comprise any appropriate high-powered solid-state switching device. The control system may be a computer; however, this is merely exemplary of an appropriate high-powered control system, which is within the scope of the application. For example, but not by way of limitation, the control system may include at least one of a silicon controlled rectifier (SCR), a thyristor, MOS-controlled thyristor (MCT) and an insulated gate bipolar transistor. The control system also may be implemented as a single special purpose integrated circuit, such as ASIC, having a main or central processor section for overall, system-level control, and separate sections dedicated performing various different specific combinations, functions and other processes under control of the central processor section. It will be appreciated by those skilled in the art that the control system also may be implemented using a variety of separate dedicated or programmable integrated or other electronic circuits or devices, such as hardwired electronic or logic circuits including discrete element circuits or programmable logic devices, such as PLDs, PALs, PLAs or the like. The control system also may be implemented using a suitably programmed general-purpose computer, such as a microprocessor or microcontrol, or other processor device, such as a CPU or MPU, either alone or in conjunction with one or more peripheral data and signal processing devices.
In use, the blade radial deformation monitoring system 20 may operate as follows. While this example of operation will relate to measuring the deformation of turbine blades 9, those of ordinary skill will recognize that the same general operation methodology may be applied to compressor blades 5. The proximity sensors 22 may take an initial measurement of each of the turbine blades 9 during the startup of the gas turbine 2. As one of ordinary skill in the art will appreciate, surface differences of each of the blades may identify each particular blade to the control system by the profile measured by the proximity sensors 22. Specifically, the minute surface differences of each of the blades may allow the control system to identify the individual blade and, thus, track the deformation of each individual blade. The initial measurement may indicate the initial length of each of the turbine blades 9. This may be determined by the known size and position of the rotor 11 and the distance measured from the proximity sensor 22 to the tip of each of the turbine bladed 9. That is, from these two values the length of the turbine blade 9 may be calculated. The initial measurement data may be stored by the control system.
As the gas turbine 2 operates, a later or second measurement may be taken. These measurements may be taken periodically; for example, they may be taken every second or every minute or every hour or some longer period. The second measurement may indicate the length of each of the turbine blades 9 at the time of the measurement. Again, this length may be determined by the known size and position of the rotor and the distance measured from the proximity sensor 22 to the tip of the turbine blade 9. From these two values the length of the turbine blade 9 may be calculated. The second measurement data may be stored by the control system.
The control system may process the measurement data to determine if the turbine blade 9 has deformed in the radial direction, i.e., whether the turbine blade has “stretched” during use. Specifically, the control system may compare the second measurement to the initial measurement to ascertain the amount of deformation or creep that has occurred. The control system may be programmed to alert a turbine operator once the deformation reaches a certain level. For example, the control system may provide a flashing alert to a certain computer terminal, send an email or a page to a turbine operator or use some other method to alert the turbine operator. This alert may be sent when the level of deformation indicates that the turbine blade 9 is nearing or is at the end of its useful life. At this point, the turbine blades 9 may be pulled from the gas turbine 2 and repaired or replaced.
As stated, the blade radial deformation monitoring system 20 may include one or more proximity sensors 22. As illustrated in
As stated, in some embodiments, only one proximity sensor 22 may be used. In such a system, it may be advantageous to used conventional rotor probes, such as a Bently probe, to determine rotor position. The rotor probes may be positioned at any point on the rotor and may measure the actual radial position of the rotor in real time. As stated, it will be understood by those skilled in the art that the rotor may displace radially during operation. This displacement may appear as deformation of the blades if the actual rotor positioning is not taken into account. If, on the other hand, the actual rotor displacement is calculated by the rotor probes, the control system may calculate the actual deformation of the blades.
In some embodiments, the proximity sensors 22 may be located such that they measure axial deformation. As illustrated in
Similar to the blade radial deformation monitoring system 20, it may be advantageous for the blade axial deformation monitoring system 30 to have multiple proximity sensors 22 spaced about the circumference of the stage. The advantage of having multiple sensors is that the relative position of the rotor may be determined and accounted for in determining the actual axial creep of the blades.
As illustrated in
In some embodiments, as described below and illustrated on
As one of ordinary skill in the art will appreciate, conventional proximity sensors have a short range of operation. Thus, when used in conjunction with a tip shrouded turbine blade, as the one described above, the proximity sensor 22 generally must be aimed such that it measures the distance between itself and the seal rail 66, which, as already described, extends radially outward from the tip shroud 64. In other words, the distance between the turbine casing 12 or stationary shrouds (where the proximity sensors may be mounted) and the outer surface of the tip shroud 64 may be too great for conventional proximity sensors to take accurate measurements, thus requiring the proximity sensor to be aimed at the seal rail 66.
As one of ordinary skill in the art will appreciate, proximity sensors measure the distance between itself and an area on the surface of a nearby object, i.e., not a single point on the nearby object. This area may be called the “area of measurement” and, in general, is circular in nature. The width of the circular area of measurement generally is wider than the width of the seal rail 66. Thus, measurements taken in this manner include a measurement of the distance to the seal rail 66 as well as measurements of the surrounding area. This situation decreases the accuracy and quality of the readings. Poor readings of this type may make it difficult or impossible to accurately distinguish between each of the turbine blades. Of course, this result may make it impossible to track the creep for each of the individual turbine blades in the stage, which for reasons already discussed is desirable.
In some embodiments, the area of the outer face of the target pad 50 may be similar in size to the area of measurement for the proximity sensor 22. Thus, when properly aligned, the area of measurement for the proximity sensor 22 may be approximately “filled” by the outer face of the target pad 50 when the target pad 50 passes by the proximity sensor 22, which will allow high quality readings to be taken. Such readings may allow the proximity sensor to more easily distinguish the different turbine blades in the stage, thus allowing the creep for each of the turbine blades to be tracked over time. In some embodiments, each target pad 50 may be configured to have a distinguishable elevation profile when read by the proximity sensor 22. In this manner, each of the turbine blades may be easily and accurately identifiable when its target pad 50 passes by the proximity sensor 22.
From the above description of preferred embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.
