Q & A

"Although we have a critical limit of 1000 ppm for moisture levels in our gearboxes, we still see traces of emulsified or even free water in the oil, usually at low ambient temperature conditions or when the gearbox has stood for some time. Why is this?"

While a 0.1% by volume of water target is a lot better than many systems currently operate at, commercial laboratories that screen for water with FTIR usually report the result as water at <0.1% or less than 1000 ppm. Unfortunately, water exists in 3 states, dissolved (beneficial), emulsified or foggy, and free water (as in rain). It is the latter two states that cause most of the damage to the lubricant and machine. However, the point at which water goes from a dissolved state to an emulsified or free state (above the saturation point) varies with temperature. While typically an oil may have a saturation point of 400 ppm at 40°C, this can go as high 1000 ppm or more at higher temperatures, or drop as low as 100 ppm or less at lower temperatures. During operation, the temperature is typically higher, but once the system cools or operates in low ambient conditions, the saturation point may be much lower and while the moisture by volume is in target, emulsified and free water still exists causing potential harm.

Establish the worst-case scenario temperature condition when the machine is at rest and a corresponding saturation point. Then, set the target based on that ppm level and use the Karl Fischer test to get a lower than 1000 ppm reading. Alternatively, check the moisture level on-site with the hotplate crackle test. Also consider using a relative humidity monitoring tool and ensure that the target is at around 50 percent RH or lower. However, do allow for fluctuations in the reading as the system operating and ambient temperature conditions vary.

Success Stories

Robert Brockway at Southern California Big Creek hydro-generating facility helped implement a lot of changes in the lubrication program for some impressive savings and reliability improvements:

• Installation of circulating pumping systems and filters - regular, full-time filtration systems were installed on critical fluid systems.

• Use of progressively finer filtration - Beginning with 25 micron filters, working down to 3 micron filters.

• Setting aggressive cleanliness targets - Initial targets of ISO 16/13 were set for the systems. These targets were achieved and re-set to ISO 14/11. These targets were achieved and re-set to ISO 13/10.

• Implementation of lubricant condition monitoring - On-site monitoring of particle counts, viscosity and moisture screening to ensure that the oil is clean and healthy and to identify abnormal wearing conditions.

Results: At just one facility over 350 inspection related man-hours, not to mention elimination of bearing reworks, lost productivity and other problems caused by opening systems for inspection. Impulse generators haven't been opened for inspection in over two years.

At the Eastwood Power Station, an underground pumped/storage hydro facility, contamination control has really paid off. Historically, dirty oil was the cause of frequent stiction and failure of the hydraulic shuttle valves. In addition to labor, at peak times, repair costs can be as high as $200 per MWH in lost production. Since installing fine filtration and on-site contaminant-monitoring, only one failure has occurred. This improvement has saved hundreds of man-hours. In time, it will yield hundreds of thousands of dollars in increased profit to the organization.

Do you have a Success Story you want to share with Lube-Tips readers? Send your story to webmaster@noria.com.

Today's Tip

• Put a permanent label on each pump and gearbox in your plant stating the type of oil it takes and what the normal capacity is. This reduces the frequency of accidentally adding the wrong oil to a piece of equipment.
  
  (Tip submitted by William Jacobyansky, Plant Engineer, Temple-Inland Forest Products Corporation)

Each tip published will earn the sender $10. Send your tips to webmaster@noria.com or fax to 918-746-0925.

Book Bits

From the book "Sourcebook For Used Oil Elements":

Unfiltered or poorly filtered oil eventually results in growing concentrations of wear debris. The problem is mutually compounding in that the dirtier the oil the more contaminated the oil continues to become from internal wear debris production and destruction to contaminant exclusion seals. While it is always good advice to maintain clean lubricants from a proactive maintenance standpoint (affirmative action), it is equally good advice for predictive maintenance (early wear detection). A failure to do so usually leads to the alarm signal effectively being "lost in the sauce." This concentrated debris results in a high noise threshold, and when an incipient wear signal occurs it will write "in the noise" and be lost (signal-to-noise is less than 1:1). This is a persistent problem with splash-fed gearing, crankcase lubes, and bath lubricated bearings.

Conversely, a clean oil provides not only a healthy and unabrasive lubricating environment but also allows the wear signal (incipient debris generation) to write above the noise level (signal-to-noise is greater than 2:1, for example). When the fluids are maintained clean and if sampling is carried out in live zones (before filters, on bearing drain lines, and at turbulent fluid zones) the early detection of wear anomalies is typically achieved. There is often a need for the routine use of portable filtration systems or retrofitted side-loop filters.

For more information about the book "Sourcebook For Used Oil Elements" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=26

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Lube-Tips is published by Noria Corporation. Oil Analysis and Lubrication Experts