Tube failures in aging steam plant surface condensers, feedwater heaters, and oil coolers are a significant reliability problem for the electric power industry. Tube failures can also result in an increase in replacement power costs. In addition, condenser leaks from failed tubes have potentially harmful effects on major components such as steam generators and turbines. To reduce the number of tube failures and consequent leakage, periodic maintenance programs have used the nondestructive evaluation (NDE) method of eddy current testing (ET) to inspect the condition of the tubes from the water side. This NDE method can identify tubes that have experienced major degradation and should be plugged to prevent in-service failure. Variability of inspection results and difficulty in inspecting some types of tubing (Monel, carbon steel) have caused many utility sites to question the value of inspection of heat transfer tubing from the water side. Recognizing these problems, advanced ET systems have been developed that use multi-frequency, remote field, and digital data processing techniques to inspect a variety of tubing materials and produce on-site, computer generated inspection reports. These results have been used to determine tube plugging, replacement, and inspection intervals.