PSI - Issue 58

Mirjana Opačić et al. / Procedia Structural Integrity 58 (2024) 87 – 94 M. Opa č i ć et al. / Structural Integrity Procedia 00 (2019) 000–000

89 3

Extensive ultrasonic testing, performed using Phased Array (PAUT) Taheri et al (2019) and Time of Flight diffraction (ToFD), Sinclair et al (2010) techniques revealed the presence of a defect within the middle section of the weld metal in one of the vertical welded joint, with a length of 75 mm, and depth of 20 mm. This defect, which was assumed to a crack, was located inside the wall, 18 mm away from its outer surface. This was a particularly interesting case, since cracks which typically occur in these cases are on the surface. 3. Ultrasonic testing of pressure vessel 970 Ultrasonic testing represents a somewhat complex, but very reliable NDT method, which can detect defects throughout the entire thickness of the welded joint, by generating ultrasonic waves which travel through the material and are then deflected by the opposite surface of the weld, or by a defect, back to the transducer. Signals recorded by the UT equipment can then be used to determine the location and size of potential defects, although they cannot always determine the exact type of defect that was detected. In more recent years, more efficient and accurate UT methods have been developed, including the aforementioned PAUT and ToFD, both of which were used during the regular non-destructive testing of pressure vessel 970. PAUT method involves a transducer with multiple crystals, which can emit multiple ultrasonic waves at once, under different angles, providing a more detailed image of the inspected object (a welded joint in this case). For pressure vessel 970, testing was performed in accordance with the acceptance criteria defined by standard SRPS EN ISO 19 285. Sonatest Veo+ device was used, and the results of this test can be seen in Fig. 2. It can be seen that this technique provides far more detailed information about defects inside welded joint, compared to conventional ones.

Fig. 2. Location of defect 5.6 in the pressure vessel 970, as detected by PAUT.

ToFD technique, on the other hand, uses two transducers, one of which serves as the ultrasonic signal receiver, and measures the time required for the waves to reach it in order to determine the location of potential defects. An example of the results obtained using this method can be seen in Fig. 3 below.