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Readers Challenge    September 8, 2004

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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