Lloyd's Register Pioneers Vibration Monitoring Techniques
Lloyd's Register of Shipping has pioneered the use of vibration monitoring of steam turbines as an alternative to the usual practice of dismantling such machinery for visual examination at the time of the first periodical survey.
Apart from the financial benefits to the owner or operator of the ship, there are possible technical advantages in not disturbing a turbine at an early stage in its operating life.
Although Lloyd's Register's Rules have provided for vibration monitoring of steam turbines since 1971, the problem has been to devise satisfactory equipment and methods which would provide information at least equivalent to a visual examination.
Lloyd's Register's Technical Investigation Department has considerable experience in the field of vibration monitoring of marine machinery and, in association with the BP Tanker Co. Ltd., and Denholm Ship Management, has carried out first periodical surveys using this alternative method on the oil tanker British Scientist and the ore/oil carrier Nordic Conqueror.
In the case of the British Scientist, the owners, BP Tanker Co. Ltd., subsequently decided, for other reasons, to open up the turbines, thus affording an opportunity to compare the predicted condition based on vibration analysis with the actual condition determined by visual examination.
The correlation of the results was found to be very good and confirmed that the method used was basically sound, and a viable alternative for surveying steam turbines.
Lloyd's Register agrees to the vibration monitoring method of survey, provided the following conditions are met: 1. The turbines are fitted with rotor position indicators as a permanent feature of the installation.
2. Records of vibration readings obtained during the preceding 12 months are available for analysis.
3. Complete sets of vibration records on the forward and after bearings of each turbine are to be taken during part power and full power sea trials using portable vibration analysis equipment.
The readings at the bearings are to be taken in the horizontal, vertical and axial directions.
4. The arrangements for the operation of the machinery with one turbine out of action are found in order and suitable for being readily fitted in an emergency.
5. The surveyors are fully satisfied from the full power trial that the turbines remain, as far as can be ascertained, in good working order.
6. The turbine rotor bearings, thrust bearings and flexible couplings are to be opened out after completion of the vibration monitoring exercise.
Lloyd's Register surveyors examine the vibration monitoring techniques to be employed, ascertain the vibration characteristics of the main turbines and assess the full power trials.
Lloyd's Register has the necessary technical equipment to carry out vibration measurements aboard ships, and the capability for analyzing the results, using the Society's own minicomputer or real-time analyzer.
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