New Approach To Torsional Vibration Monitoring
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This paper presents a summary of the authors' experience gained from implementation of model-based monitoring systems for LNG string vibration. The development of a novel train torsional vibration monitoring approach utilizing system modal analysis and lateral-torsional coupling in geared systems has been reported. A number of recent Root Cause Analysis programs related to turbocompressor string operation problems (LNG production) have faced barriers due to lack of adequate torsional vibration monitoring solutions. As the machinery problems associated with abnormal levels of train torsional vibration become more frequent, the incentives for the Oil & Gas industry to address the need for reliable and trouble-free cyclic torque evaluation gain ground. This constitutes a demand for a robust, reliable and accurate torsional vibration monitoring approach acceptable as a practical solution. Contemporary, industry-wide accepted measurement technologies (strain gage with telemetry, optical probes, laser) fit the test needs well but their lack of ruggedness and durability as well as problematic installation impacting machine operation do not permit their consideration for long-term monitoring applications. The authors present a methodology which allows evaluation of alternating torque amplitudes in different string sections based on standard instrumentation installed on the train. The approach adopted in this paper relies heavily on the modal representation of the dynamic system being analyzed. The calculation method described utilizes the results of such analysis along with the angular vibration signal obtained from standard instrumentation installed on the train (gas turbine speed pick-up signal spectrum) and typical radial vibration data from gearbox proximity probes (when available). This means that no additional probes need to be installed to get the results. The robustness and accuracy of the proposed techniques was validated in the laboratory and benchmarked against test data from several LNG production train measurement campaigns, where the alternating torque was measured by means of standard measurement systems. The authors show the results of this verification together with prospective system applications. The symbols and abbreviations used in this paper are given in the last section.
Naldi, Lorenzo; Golebiowski, Mateusz; Rossi, and Valerio (2011). New Approach To Torsional Vibration Monitoring. Texas A&M University. Turbomachinery Laboratories. Available electronically from