In service inspection (ISI) of aged power plant parts has a delicate task to provide information on presence, position, orientation and size of defects in material. As far as results of ISI are just a starting point for elaborate procedure of life assessment or risk analyses, the accuracy and reliability of these results are particularly important. Time of Flight Diffraction (TOFD) technique is regarded as one of ultrasonic techniques capable to fulfil required precision, being approved in nowadays routine inspection of retaining rings or LP turbine rotor discs. Apart from these, usually highly automated inspections, a manual TOFD testing designed for particular plant component reveals reliable and useful defect information as well. In this work, results of TOFD inspection of turbine inlet casing are presented. The component was inspected subsequently during several years up to the point of substitution by a new one. Gained TOFD results are compared with results of visual and metallographic examination of samples cut out from the casing. Key words: NDT, power plant industry, castings, TOFD