Various non-destructive testing techniques are employed for examination of these critical components with the aim of detecting such potential defects. While most of the methods like visual, fluorescent magnetic, eddy current, ultrasonic and other electro-magnetic examinations employed, sound banal, the actual techniques applied are specifically evolved to suit the detection of the characteristic defects. Such tests were carried out on various thermal power plant components at more than 30 sites in India. This paper highlights these specialised NDT techniques.

Long rigid boroscopes of 3-5 meters length are employed for examination of rotor bores for the presence of surface breaking defects. Fibroscopes are employed for detection of ligament cracking in boiler header pipes.

Specific techniques of wet fluorescent magnetic particle examination are employed for exterior as well as bore examination of rotors, discs, blading, casings, valves, superheater headers etc.

Borosonic examination is conducted on the rotors using a semi- automated equipment for detection of various defects near the bore surface as well as in the volume of the rotor.

Disc scanning technique using manual mode as well as semi- automated equipment are used for detection of radial-axial stress corrosion cracking on the hub surface of shrunk fit discs.

Retaining rings, which are one of the highly stressed components in the generator, are subjected to manual as well as automated scanning for detection of stress corrosion cracking particularly near the shrunk fit area. A PC based pulser receiver and scan controller module in conjunction with a specially designed scanner assembly, is recently developed to obtain a C-scan presentation from this critical component.

Eddy current examination using edge and surface scanning transducers, is employed for detection of surface breaking defects in the turbine blading and rotor bores. Also multi- frequency techniques are employed for examination of condenser and other heat exchanger tubes.

Electro-magnetic core imperfection detector (ELCID) is employed for detection of insulation break downs in the stator core laminations. Various defects detected in all the above tests are characterised with respect to their size, shape, location, distribution, nature etc., and this information is used for further analysis employing fracture mechanics approach for remaining life assessment.