The reliability of facilities under long-term operation, that is to prevent trouble or accident, is one of the most important matters in the field of petroleum and petrochemical plants. For this purpose, some kinds of non-destructive inspection methods are carried out periodically to detect damages or degradation of material. Moreover, to enrich the reliability of safety operation of the plants, continuous monitoring methods to detect material degradation without mistiming are required. Recently, ultrasonic method has been developed as a key technology to detect and evaluate the damage of materials. One of the advantages of ultrasonic technique is to obtain much information about microstructure change due to material degradation when ultrasounds travel through the material. Further, ultrasonic technique has also the potential ability to be applied for continuous monitoring methods. The objective of this study is to accomplish monitoring methods of creep damage using ultrasonic technique. A novel technique to acquire the ultrasonic data during uni-axial creep test is investigated as the first step of monitoring of creep damage. As a result, it is confirmed that the sound velocity in time domain decreases gradually in creep acceleration stage which starts at the creep life fraction of 0.6 and the gravity frequency in frequency domain begins to increase at the creep life fraction of 0.8. Therefore, the possibility to monitor the creep damage under continuous operation by ultrasonic technique is suggested.

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