NDTsi 2001 Session: Major Component Inspection I-IV
Examination of the Ultrasonic Testing System for Dovetail of Turbine Rotors
S. Morimoto, Toshiba, Japan
ABSTRACT
It has been reported that some axial cracks appear at dovetail of low-pressure turbine rotors. And we've performed manual ultrasonic testing to detect such cracks without removing blades. However, the usual method takes long time and the accuracy of detecting defect is not good enough. Furthermore it is difficult to discriminate the crack indication from the indication due to the rust or pitting. Then in order to resolve those problems, we suggest the new inspection method that uses 4 transducers and evaluates the B-scope in stead of A-scope. As usual UT system is applied only for wheels that surfaces are parallel each other, we made some types of test piece with different shapes of wheel and dovetail. In this presentation we'll report the result of verificational experiment. We use 4 transducers and inspect a dovetail using pulse-echo method from 4 directions at the same time, furthermore we can take 2 ways of pitch-catch method. We turn the rotor after setting the scanner on it and we can inspect a stage 360 degrees continuously. We evaluate the result using a B-scope, the indication patterns from a crack and rust or pitting are different. For the test pieces with different shapes of wheel, we made new UT scanner and applied for them and succeeded to detect artificial cracks. We made some artificial cracks at some types of dovetail and carried out the experiment using the new UT instrument. The main result is shown as follows: (1) The detectable minimum size is getting much smaller than usual method. (2) We can discriminate between the indication from a crack and that from rust or pitting. (3) The UT scanner can be applied for some types of slanted wheels. (4) We can know if the detected crack is equal or bigger than the first hook or not. (5) The system can make the testing time short.
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
