METHOD AND APPARATUS FOR DETERMINING GEOMETRY DEFORMATION IN ROTATING COMPONENTS

A method is provided for measuring geometry deformations of a turbine component, rotor groove or blade root. The method includes providing the turbine component, rotor groove or blade root, respectively, with at least one measuring mark; using the at least one mark as a reference point in determining, in a first measurement, a length on the turbine component or rotor groove or blade root, respectively, before placing the turbine into service. The method also includes operating the turbine for a period of time; determining, in a second measurement, the length on the turbine component, rotor groove or blade root, using the at least one measuring mark as a reference point, after said operating period; comparing the measured lengths of the first and second measurements; and determining an amount of creep deformation in the turbine component, rotor groove or blade root, respectively, based on a difference between the measured lengths.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG. 2, a rotor14is provided with rotor grooves for receiving respective rotor blades. A fir tree attachment part between adjacent grooves is indicated generally by reference numeral15. The grooves are shown having a general fir-tree configuration to accept a respective root of a blade (not shown) in a conventional manner. Although a fir-tree configuration is shown, it should be understood that the invention can be applied to other types of configurations, e.g. hammer root, straight and curved fir-tree, etc. The groove includes (seeFIG. 3) non-contact surfaces18and contact surfaces19as well as a bottom portion17(FIG. 2).

According to the invention, the fir tree attachment part15and adjacent grooves are marked in various locations on their surfaces with measuring marks20. These measuring marks20are preferably permanent and are formed by laser engraving with a laser engraving tool21(FIG. 2), or other suitable method. The measuring marks20serve as reference points for carrying out first and second measurements in order to determine any possible creep after the rotor14has been used. The marking of the fir tree attachment part15and rotor grooves by laser engraving or other suitable method should be performed preferably at the time of manufacture of the rotor14. It should be noted that a blade root could also be marked in a similar fashion. The positions of the measuring marks20are specific to the situation and are placed on faces where low stresses are exhibited. By placing the measuring marks20on low stress faces, cooling and mechanical behavior of the rotor or blade are not affected.

The distribution of the measuring marks20is shown in greater detail inFIGS. 3-5, which depict the views along arrows A-C inFIG. 2. The measuring marks20are placed in such positions and are sized so that they are recognizable to the naked eye during periodic inspections. As a result, at every inspection of the machine the pattern is exactly measured and deformations are identified by comparing the respective measurement results with prior measurements. The measurements are generally performed by optical or laser measurement methods, for example by means of an optical sensor22(FIG. 3). By ensuring that the measuring marks20are identical at each measurement, a more accurate measurement, as compared with current methods, is possible. Owing to this greater accuracy, risk predictions of creep damage for rotors are greatly improved.

In the method of the present invention, at least one measuring mark is provided on the turbine rotor groove (or blade root), and using the at least one measuring mark as a reference in determining in a first measurement a length on the rotor groove (or blade root) prior to the turbine being placed into service. The turbine is then placed into service for a period of time and afterwards, a second measurement, using the at least one measuring mark as a reference, of the same length on the rotor groove (or blade root) after operating of the turbine blade for the period of time is determined. The second measurement is compared to the first measurement, and an amount of creep deformation in the rotor groove (or blade root) is determined based on a difference between the first measurement and the second measurement.

The method of the present invention provides a fast and reliable way to obtain important and more accurate field data, while minimizing down time. The methodology of the method can be applied in all types of rotor grooves and blade roots independent of the design. Moreover, the method can also be applied to other components, e.g. compressor, gas turbine or steam turbine casings, in which other types of measurements, e.g. bending or ovalization, are carried out.

It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications which are within the spirit and scope of the invention as defined by the appended claims; the above description; and/or shown in the attached drawings.

LIST OF REFERENCE NUMERALS