Abstract

Vital components of power plants (rotors, shrunk-on discs, retaining rings, casings etc.) are exposed to very hard working conditions what causes crack initiation and their sometimes very rapid growth. Estimating of remaining life, what includes in service inspection (ISI) of these components, requires accurate sizing of flaws, because of calculating crack propagation and/or crack propagation monitoring. In both cases it is important to size cracks with accuracy less than 1 mm.

Technique justified as superior for sizing the defects is called Time of Flight Diffraction (TOFD). It can be performed manually, with standard ultrasonic equipment, observing changes in A scan, but to achieve its full effectiveness and accuracy, it is necessary to have adequate equipment to obtain B or D scan of unrectified signals.

This paper describes the principles and abilities of TOFD technique, as well as comparison between results obtained by standard and sophisticated equipment on some laboratory samples as well as on generator retaining ring.

Keywords: Ultrasonic Testing

Source: Conference Proceedings of the 4th International Conference of the Slovenian Society for Nondestructive Testing, 24 - 25 April 1997, Ljubljana, Slovenia.
Pages:41 - 50

Publisher:
Slovenian Society for Nondestructive Testing, Faculty of Mechanical Engineering, Askerceva 6, SLO 1000 Ljubljana, Slovenia. Tel +386 61 177 12 03, Fax +386 61 218 567, Email: janez.grum@fs.uni-lj.si.