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

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This has inspired numerous work Aranđelović et al (2021), Vučetić et al (2022), Sedmak et al (2015), Jeremić et al (2021), Jeremić et al (2020), which often combined experimental tests, non-destructive test methods and/or numerical analysis via finite element method. The case which will be presented here involves a pressure vessel denoted by number 970, which was recently examined using state-of-the-art ultrasonic testing (UT) techniques. These tests have revealed certain defects, one of which was particularly interesting - 75x20 mm flaw located inside the weld metal of the vertical welded joint. While the pressure vessel operated without any issues, it was decided to perform additional analyses in order to confirm that it is still safe for use. This involved the development of several numerical models, based on the data provided by the UT results. In order to ensure a conservative approach, it was assumed that the detected defect (which was labelled as 5.6) was a crack, i.e., the worst-case scenario was adopted. Initial models were made with and without a crack and compared to each other. After it was determined that the presence of the crack did not have any influence on the stress levels and distribution, another model was created, with different boundary conditions, since in the initial case the crack was located very close to the constrained part of the model. 2. Pressure vessel 970 description Pressure vessel in question is shown in Fig. 1. It was made of Nioval 50 steel, with EVB 65 used as filler material, due to its favourable mechanical properties. Mechanical properties of both materials were used as input data for the numerical simulations and will be given later in the text. Characteristics of the pressure vessel 970 are given below:  design diameter: Ø 2200 mm,  height: 4485 mm,  volume: 13 m 3  wall thickness: 50 mm,

 working pressure: 7.7 MPa  design pressure: 8.1 MPa

Fig. 1. Pressure vessel 970 (left) and a more detailed view of the welded joint areas where ultrasonic testing was performed.