# Investigation of Failure Causes of Oil Pump Based on Operating Conditions
## 7 Concluding Remarks  
In the present study, the main cause and the mechanism of failure for major components were analyzed on a three-axis screw-type pump, which is normally used in the ship's engine room. The frequency of failure was analyzed using FFT, and more precise results were obtained by performing STFT on the database. More than 200 databases were built with data for the core parts of the oil pump; the data represented operation under both normal and abnormal conditions. The results obtained from this study are summarized below:  
1. The failure modes and mechanisms of each part of the pump, such as the bearing, coupling, sealing, and screw, were analyzed using various studies and an accident database.
2. A test bed was established to implement each major failure characteristic and the acquired data considered the pump's operating conditions.
3. From the results of the FFT for the motor bearing, the contamination condition showed significantly larger amplitude near 400-450 Hz than the case with an absence of lubrication.
4. In the case of the misalignment of the coupling, the amplitude significantly increased in the overall frequency ranges compared with the elastomer breakage case. In particular, the amplitude near 550-600 Hz significantly increased.
5. For the screw of the pump, the amplitude increased significantly in the overall frequency ranges near 400-550 Hz in the case of the cavitation state compared with the wear dependence of the screw.
6. From the results for the sealing, the overall amplitude for the abnormal status increased in the random frequency region. However, most of the amplitude was below 0.1 mm/s2, which is relatively low compared with the other core parts such as the bearing, coupling, and screw.
7. STFT was performed considering the time unit for the extreme scenario of the abnormal condition, such as the contamination state of the bearing, under various conditions of the coupling, and finally for the cavitation of the screw.  
Figure 13: STFT for abnormal state due to the cavitation.  
Data, such as for the normal and abnormal states of various core parts of the oil pump, were collected in multiple ways and are still being collected. The STFT can analyze frequency characteristics effectively, but we need to efficiently analyze abnormal signals. Therefore, as a follow-up study, research techniques will be developed to analyze the abnormal signals much more effectively using STFT. In addition, we plan to establish a dynamic database for failure conditions and continue to prove reliability based on this database. The data verified through this study are expected to serve as the basis for developing failure diagnosis and prediction algorithm models to improve ship integrity management technology.  
Conceptualization, J.-J.L. and Y.K.; methodology, T.L. and M.-S.K.; investigation, J.-W.P. and J.-H.K.; writing--original draft preparation, D.O., J.-J.L. and Y.K.; resources, T.L. and J.-H.K.; writing--review and editing, M.-S.K., H.-J.T. and [PERSON]-W.P.; All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (2022400000090). This research was supported by Korea Institute of Marine Science & Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries, Korea (20200455). This research was supported by Korea Institute of Marine Science & Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (20220603).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.