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Bewildering Oil Analysis Results
Muhammad Adam B. Ruslan, Manager cbmXpress, Metalux
We must take note that for Particle Count result, it
will give in 3 size ranges, >4/>6/>14 micron.
While in elemental spectroscopy it will the largest size
detection limits will be 8 micron, if we are using Rotating
Disk Excitation (RDE) Spectroscopy.
In Steam Turbine systems, if we are having high Particle
Count result, while Elemental result shows none wear metals
and Silicon number, possiblity of particles that contribute
to the high Particle Count results is wear debris particles.
This wear debris particles can be from 2 sources, bearing
systems wear particles or pipe corrossion particles.
Anyway, it is more likely to be from an abnormal wear
debris particles from the bearing systems. Usually for
steam turbines, as most of the bearing are journal bearing,
the abnormal bearing wear likely happen due to 3 body
abrasion. Hard abrasive particles at a fluid film size
clearences trapped in between 2 bearing surfaces and this
lead to an abnormal wear particles generation, likely
to be cutting wear particles. This particles are large
enough to be missed by elemental spectroscopy test but
detected in Particle Count test.
Also particles like black oxides could be the possibilities
in contributing to the high Particle Count results. The
particles are formed due to insufficient lubrication between
the 2 bearing surfaces. As mention, the water presence
is between 30-40 ppm, this amount of water can contribute
the wear particles to formed rust or red oxides. It is
hard and abrasive in nature. This also likely to be the
source of high Particle Count result.
The next steps to determine the root causes of the elevated
particles counts is to test for Wear Particles Analysis,
both Direct Reading Ferrography (DRF) test and Analytical
Ferrorgraphy (AF) test. Using Direct Reading, if we see
high Wear Particles Concentration (WPC), with high Percentage
of Large Particle (PLP). We can confirm the bearing systems
have an abnormal wear generation.
Using AF, we can confirm the type of wear modes, if is
cutting wear with less than 15 micron in size, it confirm
the abrasive contaminants had enter the bearing systems
and generate the wears. Root cause of the problems are
the hard abrasive particle that are of the bearing clearances
size, this particle need to be removed by doing offline
filteration, using a fine filter elements i.e 3-5 micron
with beta rated 200.
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