Non-destructive examination plays an essential role in maintenance programmes to assure operation of industrial plants. Life of radiant catalyst tubes of reformer units exposed to high pressure and temperature is limited by creep damage. Present inspection techniques offer unreliable results, removing tubes from service in a very conservative manner or occurring unexpected tube ruptures. Existing ultrasonic methods rely on the analysis of ultrasonic amplitude of the received signal((1)). Due to the material coarse structure, this produces qualitative assessment as well as, on occasions, unreliable results. To overcome these limitations, a multi-interrogation ultrasonic technique and correlation of several parameters such as attenuation, energy and tube diameter with material features is devised. This paper describes the principles of the ultrasonic method for creep, damage detection as well as details of the inspection system. Results of measurements performed on representative damaged specimens are also shown, including relationships between ultrasonic and metallurgical parameters.
