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.
