PSI - Issue 82

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2026) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2026) 000–000

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 82 (2026) 220–226

© 2026 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 ICSID organizers Abstract Fracture of the turbine rotor thrust collar is a very rare failure. However, such a failure can occur due to some serious malfunction in the operation of the turbine. In this paper, the root cause of the rotor thrust collar fracture, which occurred in the history of a 35 MW steam turbine, is analyzed. The analysis was carried out based on the facts found and using numerical simulations in the Ansys software package. The cause of the fracture was determined to be high-cycle fatigue as a result of cyclic loading and a significant notch effect at the root of the shaft-collar transition radius. Cyclic loading was a consequence of the non-uniform loading of the collar over the surface, which was the result of incorrect sliding of the front bearing housing during the thermal expansion of the turbine casing in the start-up phase. The turbine rotor was repaired so that the cracked thrust collar was removed by machining, and the new collar was shrink fitted onto the rotor shaft. After the repair and the final assembly, the turbine was put into operation without any observed deficiencies. © 2026 The Authors. Copy from the contract: 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 ICSID organizers Keywords: Fracture; Thrust Collar; Highcycle Fatigue; Turbine Rotor; FEM; Stress Analysis 1. Introduction The purpose of the turbine thrust bearing is to ensure an adjusted axial position of the rotor in relation to the stationary elements of the turbine. To achieve this, it must be able to withstand axial load due to steam pressure and blade reaction. The most common thrust bearing is a fluid film bearing with tilting pads. The pads are usually steel 8th International Conference on Structural Integrity and Durability (ICSID2025) Analysis of a steam turbine rotor thrust collar fracture: root causes and repair Marko Katinić a, *, Pejo Konjatić a a University of Slavonski Brod, Mechanical Engineering Faculty, Ulica 108. brigade ZNG 36, Slavonski Brod 35000, Croatia Abstract Fracture of the turbine rotor thrust collar is a very rare failure. However, such a failure can occur due to some serious malfunction in the operation of the turbine. In this paper, the root cause of the rotor thrust collar fracture, which occurred in the history of a 35 MW steam turbine, is analyzed. The analysis was carried out based on the facts found and using numerical simulations in the Ansys software package. The cause of the fracture was determined to be high-cycle fatigue as a result of cyclic loading and a significant notch effect at the root of the shaft-collar transition radius. Cyclic loading was a consequence of the non-uniform loading of the collar over the surface, which was the result of incorrect sliding of the front bearing housing during the thermal expansion of the turbine casing in the start-up phase. The turbine rotor was repaired so that the cracked thrust collar was removed by machining, and the new collar was shrink fitted onto the rotor shaft. After the repair and the final assembly, the turbine was put into operation without any observed deficiencies. © 2026 The Authors. Copy from the contract: 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 ICSID organizers Keywords: Fracture; Thrust Collar; Highcycle Fatigue; Turbine Rotor; FEM; Stress Analysis 1. Introduction The purpose of the turbine thrust bearing is to ensure an adjusted axial position of the rotor in relation to the stationary elements of the turbine. To achieve this, it must be able to withstand axial load due to steam pressure and blade reaction. The most common thrust bearing is a fluid film bearing with tilting pads. The pads are usually steel 8th International Conference on Structural Integrity and Durability (ICSID2025) Analysis of a steam turbine rotor thrust collar fracture: root causes and repair Marko Katinić a, *, Pejo Konjatić a a University of Slavonski Brod, Mechanical Engineering Faculty, Ulica 108. brigade ZNG 36, Slavonski Brod 35000, Croatia

* Corresponding author. Tel.: +385-35-493-429. E-mail address: mkatinic@unisb.hr * Corresponding author. Tel.: +385-35-493-429. E-mail address: mkatinic@unisb.hr

2452-3216 © 2026 The Authors. Copy from the contract: 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 ICSID organizers 2452-3216 © 2026 The Authors. Copy from the contract: 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 ICSID organizers

2452-3216 © 2026 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 ICSID organizers 10.1016/j.prostr.2026.04.034