501F Vendor Spotlight: Colorless varnish? – Combined Cycle Journal

501F Vendor Spotlight: Colorless varnish?

C C Jensen

Recently, some C C Jensen customers have suffered turbine trips and typical varnish-related issues—without seeing any obvious signs of varnish.

Example: If it were only for the standard MPC test, one user could have concluded his plant’s turbine oil was varnish-free based on the excellent rating of 4 from a Membrane Patch Colorimetric Test (Fig 1). However, two more analyses gave far different results and a truer picture of oil condition:

  • An Ultra Centrifuge score of 7, which is associated with a “critical” level of varnish (Fig 2). Recall that the UC scale runs from 1 to 8, with the high score the worst possible.
  • A significant difference in the results from the two particle-count methods—optical, which counts both soft and hard particles, 25/24/13; and pore block, which counts only hard particles, 15/14/10. Note that particle counts above the high teens typically reflect a significant concentration of soft particles.

A conclusion drawn from the foregoing results: There are countless soft contaminants that can act like varnish, and no matter where they come from, must be dealt with.

For turbines running baseload or cycling where high oil temperatures are the norm, the only two options for oil conditioning/varnish removal are: filtration with selective chemical bead/resins and VRU technology, which physically removes all soft contaminants from solution and captures them in fairly inexpensive, high-absorption capacity filters (Fig 3).

Both methods work very well. While it sometimes a takes a few trials to identify the right chemical/resin to achieve the results expected, the VRU method works with any and all soft contaminants without any adjustments necessary.

As a general rule, the larger the discrepancy between a low MPC and high UC, the more soft contaminants you will have to remove. In a typical 6000-gal lube- and control-oil reservoir with varnish issues you can have less than 10 lb of varnish. In extreme cases, more than 100 lb of varnish may be removed from the oil.

Finally, feel free to share your oil analysis with Axel Wegner (axel@ccjensen.com) if you are in doubt or just want a second opinion.

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