Patent Application
20060280604
The present invention relates to apparatus and methods for inspecting the surface of cooling slots in turbine rotor wheels for defects and particularly relates to apparatus and methods for displacing an eddy current probe at constant speed along the cooling slot to optimize data collection.
Rotor wheels, for example for gas turbines, typically include a plurality of circumferentially spaced dovetails about the periphery of the rotor wheel defining dovetail slots therebetween. The dovetail slots receive corresponding dovetail shaped bases of buckets which carry the plurality of airfoils about the rotor wheel. The buckets or airfoils are often cooled by air entering through a cooling slot in the rotor wheel and through grooves or slots formed in the bases of the buckets. Typically, the cooling slot extends circumferentially 360° through the dovetails in the dovetail slots. Eddy current inspection of the cooling slot may be used to identify cooling slot surface defects. It has been discovered however that when pulling an eddy current probe along the slot, e.g. manually, the variability of the speed of movement of the probe along the slot affects the sensed data. When the data is analyzed, the detection of cracks along the cooling slot surface and their location become much more difficult to ascertain. Accordingly, there has developed a need for apparatus and methods for accurately and consistently sensing cooling slot surface defects in the cooling slot of a turbine rotor wheel.
In a preferred embodiment of the present invention, there is provided a method for inspecting a surface of a cooling slot about a turbine rotor wheel having a plurality of circumferentially spaced dovetails defining dovetail slots therebetween, the cooling slot extending circumferentially about the dovetails and the dovetail slots, comprising the steps of: disposing an eddy current probe in the cooling slot; and moving the eddy current probe along the cooling slot at a constant speed to detect cooling slot surface defects.
In another preferred embodiment of the present invention, there is provided apparatus for inspecting a surface of a cooling slot about a turbine rotor wheel having a plurality of circumferentially spaced dovetails defining dovetail slots therebetween, comprising: an eddy current probe for disposition within the cooling slot; a mounting assembly including an electric motor and a plug for disposition within a dovetail slot for supporting the electric motor outwardly of the cooling slot; a lead between said probe and said electric motor for disposition along the cooling slot, said electric motor enabling the lead and the probe to be pulled along the cooling slot.
Referring to the drawings, particularly to
Referring to
Generally, an eddy current probe, e.g. probe 30 is displaced along the cooling slot 16 and collects data reflecting surface defects in the cooling slot. It has been discovered, however, that variations in the speed of the probe passing along the cooling slot affects data collection to the extent that the data becomes shifted and distorted rendering it more difficult to accurately detect and locate surface defects. By moving the probe along the cooling slot at a constant speed, however, and in accordance with a preferred aspect of the present invention, the data collected produces substantially clearer and more accurate results. Also the test results are more consistent between different operators and reduces the human error which could lead to poor inspection results.
The present invention provides a system for moving an eddy current probe along the cooling slot 16 of the turbine wheel at a constant speed. To accomplish this, the probe 30 has a lead 32 attached to the probe at one end for drawing the probe along the cooling slot 16. The opposite end of the probe 30 is coupled to a data collection system 34 for collecting data generated by the probe. The opposite end of the lead 32 is coupled to a mounting assembly generally designated 40 including an electric motor 42 (
Referring to
The mounting assembly 40 also includes a pivot block 56 pivotally mounted to the assembly on a pivot pin 58. The pivot block 56 carries a slot plug 60 which has a distal shape generally corresponding to the base of a dovetail slot 14. It will be appreciated that by mounting the slot plug 60 in one of the dovetail slots 14 the wheels 48 and 50 of the motor assembly can be aligned radially with the cooling slot 16.
To pull the probe 30 along the cooling slot 16 at a constant speed, the lead 32 is threaded into the cooling slot 16 through a dovetail slot 14 adjacent the area of inspection. The lead 32 is then threaded along the cooling slot 16 passing along or below a certain number, for example ten, dovetails 12 and a similar number of dovetail slots 14. The lead 32 is then threaded radially outwardly into and through a dovetail slot 14 for threading between the wheels 48 and 50. The assembly 40 is mounted to the wheel 10 by inserting the slot plug 60 into an adjacent dovetail slot 14. The positioning of the slot plug 60 enables alignment of the assembly to the cooling slot and supplies stationary support for the pulling mechanism within the assembly.
Additionally and as illustrated in
The motor 42 in the motor housing assembly 40 is a variable speed motor which can be operated at a variety of constant speeds. Consequently, when the motor is set to drive the wheels at a constant speed, the lead 32 draws the probe 30 along the cooling slot 16 at a constant speed. By drawing the probe through the cooling slot 16 at a constant speed, clearer data results are achieved for enhanced detection and accurate location of defects along the cooling slot.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
