Bearing oil testing

What you need to do is find a company that performs oil analysis. You can do a web search or ask your lube oil supplier if they deal with one. (It doesn't have to be local) They will supply you with a sample kit that will have a container(s) for the oil sample and a card that you will fill out telling them the brand and grade of oil and it's applications, # hours, operating temp., etc. These kits have a return shipping box that you send to the lab where they will analyze the sample. They will send you a report on the sample and list all impurities and or contaminants found in the sample by percent or PPM content. The report should denote what is allowable in the application and what is over-limit. A good lab can also be helpful in determining the source of the contaminants but that is ultimately up to you.

Asitha,

Look for a local Caterpillar Equipment dealer in your area. They are required to have an oil laboratory in-house (at least at the home base office) and can analyze everything and provide you with test kits. They do all types of machines including aircraft so don't worry about your power plant not being a Caterpillar piece of equipment. You would look for wear metals in the oil and begin trending the wear metals with time and duty (mega watts v time v temperature, etc.). They can also tell you is the oil is still stabile, or oxidised, contaminated with water, or otherwise in good order. Should be about $25 USD or equal per test +/-.

If it were me, I would contact my counterpart at a commercial power plant. Depending on the manufacturer of the plant (i.e. GE Westinghouse), they are VERY specific on lubrication oil, filtration, etc. It is not as important to test what would be best as it is to comply with the manufacturers specifications.

I have to make certain suppositions about your turbine(s) and the generator itself, ambient situation, and several other factors to plug into your situation. To assume would be a disservice. Follow to the letter the specifications and recommendations of the power plant manufacturer. Anything short of that could lead to catastrophic failure, which is not cheap.

Hello,

You might consider monitoring the vibration signature of the power generator for bearing tones. You will be able to see bearing wear out and fatique problems on a continuous basis .

Best

Peter

Asitha,

the different subscribers have given some useful hints for checking the bearing oil quality: going for an oil analysis. I would also recommend to contact your supplier for lubrication oil.

Following results might be of interest:

- oil quality (compared to "as new"). First the viscosity is important (bearing function is based on correct viscosity). A significant change of Viscosity Index (VI) can be harmful for the bearing. The acid number (TAN) shall not exceed value 2. Anti-Oxidant content shall be observed (the laboratory should provide advises if remaining content is sufficient for further use.

- oil cleanliness. Cleanliness according ISO 4406 better or equal class "_/17/14" (or NAS class 7 to 9. Cleanliness can be improved by Micro-filtering.

- White metal (Babbitt) wear elements. Depending on Babbitt type (Sn-based or Pb-based) the max. content is tin (Sn) respective Pb. Other typical components are Sb and Cu. Interpretation of wear metal content in oil depends on used oil volume in the lubrication circuit (and number of included components which potentially can be subject to friction and wear). Practically this means, interpretations are plant-individual. It will help a lot if oil analysis are made periodically and wear contents drawn along the operating hour scale. Then you can see trends. A significant ramping up of a certain wear metal would point to a equipment examination at next possible time.

If you have self-lubricated bearings (no external oil pumps) the oil volume is very small - just the volume of bearing housing oil sump. Those small volumes typically are not analysed (analysis is as expensive as replacing the oil), except there are suspicious observations. But in that case the best action is: open the bearing and go for examinations at next possible time. This is recommended as well if oil colour would change to gray/black or bearing temperature rising with time by 10 K (compared to as new condition). Examination would give chance for bearing inside cleaning, which shall be done latest after 4 years of operation (self lubricated bearings). Oil using time can be estimated to 8000 h (bearing temperature below 80°C); 4000 h for temp. 80° and more --> self lubricated bearings.

For sleeve bearing lubrication use a petroleum based oil with an excellent recommendation to be used for steam turbine lubrication! Do not replace a petroleum based oil by a synthetic oil without contacting the bearing maker.

If you are free in selecting the bearing lubrication oil (= no other machines connected to same lube system needs to be considered) do not use SAE oils nor reduction gear oils (with EP improvers).

I am working for one of the worlds leading bearing maker (sleeve bearings for electrical machines). What we can't provide is an assistance in questions like: "I found xxx ppm Sn in the oil, what is the acceptable content?". As mentioned above, the matter is very individual and it needs a long time of experience (monitoring the oil quality) before anyone is able to separate "normal" from "suspicious" content.

Good Luck, Albert Caspers