Application of Advanced NDE Tools for Health and Life Assessment of Critical Power Plant Components During the Flexible Operation Regime

Components of power plants are subjected to different damage mechanisms like creep, fatigue, erosion, corrosion depending on their environment of operation. In present context, many of the coal-based power plants are subjected to flexible operations due to preference for renewable energy, when the latter is available. With the rapid growth in deployment of renewable energy resources, the fossil fuel-based power plants are subjected to flexible operation, which impose fluctuating stress on the components and may lead to their premature failure and affect reliability and availability of the power plant. The timely deployment of matrix of conventional and advanced NDE tools is expected to help the Power Utilities in early detection of defects before they cause forced outage of the unit. With the increasing number of units and generation capacity, it became imperative for a well-run utility to adopt such inspection technologies, which are faster, reliable, and more informative for taking timely action and decision for run, repair, and replacement of components. Many conventional NDE methods for surface and volumetric inspections have undergone rapid advancement with growth in technology. Time of Flight Diffraction (TOFD) and Phased Array Ultrasonic Testing (PAUT) are now increasingly used in the field for rotor shafts, blades, pipes and tubes inspection. The advancement in UT methods and better understanding of the damage mechanisms has led to use of UT based methods for in-situ detection of hydrogen damage in the water wall tubes. Even the conventional Radiography Testing (RT) has moved towards digital RT. Along with conventional eddy current probes, array probes are used for surface inspection of critical components like aero foil or root area of turbine blades. Similarly, more advanced tools, like Frequency Scanning Eddy Current Testing (FSECT) are now available for assessing the healthiness of the coated gas turbine blades or vanes. Advancements in the field of robotics have also been used for increasing coverage of inspection like boiler headers. MCF based system for assessing properness of Post Weld Heat Treatment (PWHT) in T-91 tube and for detection of exfoliation build-up at bends of SS tubes have also been started to be used in power plants. This review paper discusses the application of these advanced NDE methods for assessing healthiness of critical power plant components and presents some of the cases studies based on the deployment of these tools in field for different components like boiler tubes, pipes, headers and turbine blades etc., which have helped in increasing reliability and availability of power plants.