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3. The influence of defects on machine and equipment vibration, the diagnostic symptoms of defects.

Question 3.1.

 Are the diagnostic symptoms of the same defects in the same machines similar when you diagnose the machines after their manufacturing, in operational conditions and after maintenance? The question was asked by the diagnostics services of "LukOil" enterprises.

The question is answered by Alexej V. Barkov:

The operation life of any machine or its unit includes four main life stages, viz.:

  • run-in after manufacturing (repair),

  • operating without faults,

  • appearance of certain incipient defects and their development,

  • the development of sequential series of dependent defects immediately before the machine failure (degradation).


Naturally each operation life stage requires the adjustment not only of the diagnostic defect symptoms but also the diagnostic methods used for each stage. Only the second and the third stages of machine operation life from the diagnostic point of view can be considered as one and it is possible to use there the same approach.

The main problem in the first stage is to detect the manufacturing and mounting defects of the whole machine and its units. The peculiarity here is the possibility of wear defects symptoms appearance because the machine mating parts are yet not aligned. These symptoms disappear during run-in of the machine.

The diagnostic problem on the second and third stage of machine operating life is to detect its incipient wear defects and make a long term prediction of their development. The peculiarity of defect development during this period is the possibility of defect symptoms appearance and their following vanishing or decrease of the parameters describing the depth of the defect. It is the result of the further friction mating surfaces alignment even after defect appearance or the changes of the loads applied to the friction forces.

The diagnostic problem during the forth stage of operating life is to detect the dangerous situation and make the prediction of the residual service life of the whole machine or its unit. The peculiarity is the possibility of unpredictable quick defect development (immediate accident). Hence, it is necessary to control the diagnostic parameters continuously.

The diagnostic symptoms and criteria are selected according to the problems and the peculiarities.

During the forth stage are used the same symptoms as in the typical monitoring systems, viz. the optimal symptoms are designed on the basis of evaluation the vibration and noise energetic parameters. During the second and third stages the main contribution in diagnostics are made by high frequency vibration parameters and first of all the parameters of its envelope. From the diagnostic point of view the most complicated stage is the first one so here all the possible defect symptoms are used including those that help to eliminate the false symptoms of the wear defects.

Both our third generation software and means of signal measurements and analysis take into account all the main peculiarities of rotating machines' diagnostics on each type of machine operating life.

 

 

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