PSI - Issue 79

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ScienceDirect

Procedia Structural Integrity 79 (2026) 117–123

© 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of IGF28 - MedFract3 organizers Keywords: Risk based assessment, Pressure vessels, Finite Element Method, Ultrasonic Testing (TOFD and PAUT), Failure Assessment Diagram 1. Introduction Pressure vessels for compressed air in the Reversible Hydropower Plant “Bajina Bašta” (RHPP BB) in Serbia worked for 42 years before being replaced in 2024 after a long history of problems with unacceptable crack-like defects in welded joints. Numerous non-destructive tests have been performed to assess their structural integrity ever since 1999 when defects were detected for the first time by Radiographic Testing (RT) and later monitored and followed by Ultrasonic Testing (UT), as described in [1-5]. In the scope of structural integrity assessment, a novel risk-based Abstract Pressure vessels (PV) for compressed air were installed 45 years ago in RHPP Bajina Basta. After 18 years of exploitation, unacceptable defects in welded joints were found during regular monitoring by NDT. Initial assessment of structural integrity, based on conservative fracture mechanics analysis, indicated a possibility to use the vessel in regular operating mode. Monitoring in the meantime was intensified, with regular NDT examinations every 6 months, using conventional NDT methods, Ultrasonic (UT) and Radiographic testing (RT). Recently, more advanced NDT UT methods were introduced, Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD), to evaluate defect position and size more precisely. Also, the finite element method was applied to evaluate more precisely the stress state in the PV with a crack-like defect. In this way structural integrity and risk of failure was assessed more reliably. Finally, after 27 years of exploitation these PVs were replaced and welded joints with defects examined once again to get the final verdict. 28th International Conference on Fracture and Structural Integrity - 3rd Mediterranean Conference on Fracture and Structural Integrity Case study of a pressure vessel operating with unacceptable defects Lazar Jeremi ć a *, Mirjana Opa č i ć a , Aleksandar Sedmak b , Simon Sedmak a , Nikola Milovanovi ć a , Nikola Aleksi ć b a Innovation Center of Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade, Serbia b University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade, Seria

* Corresponding author. E-mail address: ljeremic@mas.bg.ac.rs

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of IGF28 - MedFract3 organizers 10.1016/j.prostr.2025.12.315