PSI - Issue 37

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect

www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 37 (2022) 263–268

ICSI 2021 The 4th International Conference on Structural Integrity Structural Integrity Analysis of a Kaplan Turbine Cover Aleksandar Sedmak a , Miodrag Arsić b , Nikola Milovanović c , Mirjana Opačić c , Branislav Đorđević c a University of Belgrade, Faculty of Mechanical Engineering, Serbia b Institute for Testing of Materials IMS, Belgrade, Serbia c Innovation Center of the Faculty of Mechanical Engineering, Belgrade 35, Serbia

© 2022 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 Pedro Miguel Guimaraes Pires Moreira Abstract During recent revitalization of Kaplan turbine aggregate made of structural steel St 3 (GOST standard), experimental investigation was performed. Base metal and welded joints were tested by non-destructive methods (NDT), and by testing of mechanical properties, including fracture mechanics parameters. Ultrasound testing (UT) indicated lack of penetration in weld metal and lamellar tearing in base metal. The latter one was in accordance with the reduced contraction of the base metal, as obtained by tensile testing, being significantly lower than the specified value. Also, fatigue crack threshold value was approximately two times smaller than expected for St 3 steel, whereas crack growth rate was significantly higher. In addition, numerical analysis of the cover was performed in different turbine operational modes to get all necessary stress distributions and enable structural integrity and life analysis. Despite significant degradation of the base metal and defects in weld joints, this analysis has shown that structural integrity of turbine cover is not jeopardized, not only because dynamic loading is just 5% higher than the static one, but also because defects in weld root are much shorter than critical crack lengths, as evaluated by LEFM calculation © 2022 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) 1. Main text Vertical Kaplan turbines are built in six hydro- power units ‘Đerdap 1’ (Kladovo, Serbia) with nominal power 176 MW. During recent revitalization and modernization of turbine aggregate A4 experimental investigation of the current state of turbine cover, made of structural steel St 3 (GOST standard), has been performed in order to analyse its structural integrity after 40 years of operation. Turbine equipment is exposed to high stresses, including residual stresses, both regular and irregular regimes. Long history of cracking and other problems with such equipment is described in [1-9], while methods how to prevent or solve problems are described in [10-17]. Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira Keywords: Structural integritz assessment, Kaplan turbine cover, Welded joint defects

2452-3216 © 2022 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 Pedro Miguel Guimaraes Pires Moreira

2452-3216 © 2022 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 Pedro Miguel Guimaraes Pires Moreira 10.1016/j.prostr.2022.01.083