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COBEM 2023
27th International Congress of Mechanical Engineering
Some Considerations about the Use of Operational Modal Analysis in Turbomachinery
Submission Author:
Luiz Antonio Vaz Pinto , RJ , Brazil
Co-Authors:
Adhemar Castilho, Antônio Carlos Troyman , Luiz Antonio Vaz Pinto, Ulisses Admar Barbosa Vicente Monteiro
Presenter: Adhemar Castilho
doi://10.26678/ABCM.COBEM2023.COB2023-0094
Abstract
The importance of using high-performance centrifugal compressors applied in CO2 reinjection in offshore platforms is fully recognized. These machines work with pressure levels above 600 bar and induce the original manufacturer equipment (OEM) as well as their users (Oil companies) to develop more and more sophisticated technologies in manufacturing processes and increasingly complex acceptance tests. The OEM knowledge has been addressed to high density gases (CO2 in high pressures) which add uncertainties in rotor dynamic stability design for these machines. Then, the number of end users who require stability tests verification has grown. There is another risk inherent in mentioned scenarios, which is not intuitive. The risk of imbalance increases on this turbomachinery. This risk is not well understood, having already been responsible for many productions loss at several offshore platforms reported as imbalance problem. It should be noted that these machines have already been approved in API 617 acceptance tests. Approval on these tests is not a guarantee of suitable performance in field. This risk is frequently referred as Design Uncertainties. In order to exemplify this anomaly, we can refer to a real case where a multinational oil company had its platform decommissioned for not being able to produce any appropriate amount of oil. This iconic case was reported as high vibration fail. After major design changes, recommended by the contracted consultant, implemented, and tested by the OEM, it was reinstalled on the original platform without any performance improvement, making field “gas-lift” operation not anymore possible. We may regard this question as being misunderstood. By other hand, there is the possibility of operating a turbomachine above its third critical, as suggested by an expert consultant. Although a similar machine can operate satisfactorily on test facility, according with API 617, there is a risk of bad vibration performance in an offshore plant, due to Rotodynamic Design Uncertainties. In API 617 this subject is not fully treated, making the equipment buyer responsible in case structural stiffness is lower than 3.5 times bearing stiffness. In this paper we suggest a treatment for this design anomaly. We are proposing a vibration monitoring system, which will allow a data record in refineries and subsequent analysis of the results using a specific framework. The real vibration values were considered in framework and the results were analyzed.
Keywords
Rotordynamics, Turbomachinery, Vibration
