PSI - Issue 82

Marko Katinić et al. / Procedia Structural Integrity 82 (2026) 220 – 226 M. Katinić, P. Konjatić/ Structural Integrity Procedia 00 (2026) 000–000

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Fig. 5. Grooves in the surface of the bearing housing.

5. Conclusions Some malfunctions in steam turbine operation are extremely rare, but unfortunately, they do occur under certain circumstances. The sudden fracture of the thrust collar described is one such example. This type of failure, although uncommon, can have serious consequences if not detected and addressed promptly. In this particular case, the failure was caused by high-cycle fatigue, which developed as a result of inadequate sliding of the front bearing housing during the thermal expansion of the turbine casing in the start-up phase. This issue arose from a mismatch between the thermal expansion of the turbine casing and the movement of the bearing housing, which prevented smooth operation during the initial heating phase. The described case is a reminder of the complexity of mechanical interrelationships within steam turbines and the importance of proper design and careful monitoring of turbine operation. This is also an example of a successful turbine repair as a result of detailed engineering analysis, an in-depth understanding of the turbine's mechanical behavior and the application of a targeted, effective technical solution. By addressing the root cause of the thrust collar failure and implementing the necessary corrective actions, the turbine was restored and returned to full operational condition. The success of the repair and the robustness of the applied solutions are evidenced by the fact that the turbine with the redesigned rotor thrust collar has been operating for more than 25 years with an accumulated service life of more than 100,000 hours. The reliable and safe operation of the turbine over this long period is an indication that even a serious failure can be resolved efficiently and qualitatively, thereby extending the service life and improving the reliability of the turbine. Furthermore, the importance of preventive maintenance for the reliable and safe operation of steam turbines is also highlighted in this case. It is crucial to carry out preventive activities both during operation and during planned turbine downtimes. Inspections and testing of the rotor during each planned overhaul, which follow a carefully and precisely defined plan, are crucial for detecting any defects that may have arisen during turbine operation. Regular monitoring of turbine operation and parameter analysis, as well as dimensional and non-destructive inspections, help in the early detection of defects, thus preventing costly and damaging failures in the future. Acknowledgements The authors express their gratitude to the company Petrokemija d.d. Kutina for providing technical documentation and useful data. References

Barella, S., Bellogini, M., Boniardi, M., Cincera, S., 2011. Failure analysis of a steam turbine rotor. Engineering Failure Analysis 18(6), 1511-1519.