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Bewildering Oil Analysis Results
Dave Yunkers, Technical Application Specialist, Analysts,
Inc.
A number of return line bearing samples from a steam
turbine show elevated particle counts. Wear metals, silica,
and water have been eliminated as to the cause or reason.
Starting with the most obvious (or easiest) I would direct
attention to the sample containers and confirm they are
ultra-clean jars with the seal covers still in place.
Next would be to confirm the samples are being drawn in
a proper manner: if a plug is being removed ensure the
area is wiped before removal and sufficient oil is allowed
to flow before capturing the sample, etc.
Lines returning to the reservoir will gather contamination
to varying degrees and particle counts cannot be reliably
'trended'. However, the question in this case is relative
to composition of the particulate, not it's varying presence.
I would want to know if the particulate is being generated
during each given lube cycle. This could be confirmed
by taking a sample at the current sample point and another
following the filter. If the filters are adequately reducing
the particle levels, we'd know the elevated levels are
being generated with each pass through the system.
Using these same samples, I would direct the laboratory
to visually identify any non-metallic contaminants present
in both samples. There are two options: (1) Ferrography,
and (2) Millipore filtration with microscopic examination.
Since there were no elevated ferrous wear metals present,
Ferrography may be limited in what will be captured on
the slide. My choice would be a membrane extraction (0.8µ)
for particulate removal and microscopic identification.
The examination should focus on identifying the size
and composition of contaminants that could include: filter
media materials, carbon (seals), hose or gasket materials,
varnish formations, lint or cloth fibers (shop towel),
etc. There could also be gels formed from an incompatible
fluid mixture (such as a glycol based fluid). These gel
formations would be detected as solid particles in a laser
detector.
Should this not provide the necessary evidence, we'd
submit a filter element for removal and a visual examination
of what is present within the media. Hopefully, these
steps would provide the answers for corrective and preventative
actions.
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