IN-SERVICE INSPECTION AND DEFECT ASSESSMENT OF STEAM-TURBINE ROTORS

For some 20 years MAN Energie have been conducting ultrasonic inspecti on of long-term service-stressed turbine rotors. This inspection serve s the purpose of requalifying a rotor to comply with the state of the art, in order to guarantee plant safety and availability even after su stained periods of operation. Nowadays the work is carried out by mean s of mechanized, computer-assisted ultrasonic inspection systems. Eval uation of the ultrasonic indications is based on the results of nation al and European joint projects extending over the last 14 years. The r esearch projects were focused on the fracture-mechanics behaviour of n atural defects in the rotors and on determining the true size of the d efects by means of manual and mechanized computer-assisted ultrasonic inspection.