Abstract: Nondestructive testing of the steam generator tubes was critical to the safe and economical operation of nuclear power stations. Eddy current testing using bobbin coil probes was fast and effective in detecting and sizing the degradation that took place in early steam generators. However, new forms of degradation had appeared in recent years that required development of more sophisticated inspection technology. Different damages of the degradation required different inspection tools. The eddy current testing and ultrasonic testing had some limitations in detecting degradation damage. The sizing capabilities for these inspection methods were particularly limited.In some cases, the uncertainties in sizing of the defects were determined by comparing with metallographic examinations of pulled tubes.