Maintenance of gas turbines: Impact and implications for NDT

Gas turbines and particularly their hot path components exhibit relatively high maintenance cost and short in-service inspection cycles, in comparison with most main components of thermal power plants. The overall share of production capacity covered by gas-fired combined cycle and CHP plants utilising gas turbines is still increasing, and the short inspection and maintenance cycles suggest corresponding strong growth for NDT services. NDT of gas turbine components is typically specified for three different purposes: within the shop during different phases of manufacturing or repairs, for user acceptance of new or reconditioned components, and for in-service assessment on the run/repair/replace decisions. The most demanding inspections in many ways are those performed in the field, as the available methods and access for the inspections can be fairly limited. Majority of the field inspections apply visual and surface techniques, but also ET and UT appear to find increasing use as they provide the potential advantage of indicating flaw depth. Examples are shown on in-service and ex-service inspections of hot-end components, particularly turbine blades and vanes.