Fault Diagnosis of Lakvijaya Power Plant: A Case Study of an Anti-Rotational Pin Failure

Abstract

Phase 1 of the Lakvijaya power plant has suffered an inherent vibration problem leading to its temporary shutdowns in 2013, 2014 and 2015. The purpose of this study is to present a hypothesis to explain causes of these vibrations, test the hypothesis and make suitable recommendations to avoid such occurrences in the future. When the shell of one of the bearings adjacent to the intermediate pressure turbine was opened for repairs in January 2015, it was observed that the anti-rotational pin of the labyrinth seal of the bearing has been broken causing the observed unusual vibrations. There are evidences to believe that this has happened in two previous occasions as well. The visual inspection of the fracture surface of the anti-rotation pin revealed that it has been failed from fatigue failure. Further, examination of the images of the facture surface obtained using scanning electron microscope indicated that the fracture has originated from the outer surface of the pin and propagated to final fracture by fatigue failure. Another region of the scanning by electron microscope image showed that the pin had been subjected to heavy deflection as well. This paper presents a hypothesis to explain how the anti-rotational pin of the labyrinth seal was failed and test the validity of the hypothesis using vibration data. Computations carried out to test the hypothesis show that the stresses inside the anti-rotational pin due to the forces exerted on it by the labyrinth seal can exceed the its fatigue strength causing its failure.