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Q & A

“We are currently selecting a new turbine oil for our steam turbine. Is the RPVOT (a.k.a. RBOT, ASTM D2272) a good indication of the relative ability of two different oils to resist oxidation?”

This is a common misconception regarding the RPVOT test. The RPVOT or Rotating Pressure Vessel Oxidation Test works by stressing the oil in an oxidating environment that includes heat, water, copper catalyst, oxygen, pressure and agitation. The test measures the length of time the oil can resist these stressing conditions before the break point is reached and the oil degrades (oxidizes). This is influenced by the quantity and type of antioxidants, the presence of natural inhibitors in the base oil, and the resilience of the base oil to oxidation.

However, because the actual conditions a turbine oil experiences in application may be considerably different than that present in the RPVOT test, there may not be good correlation between RPVOT values and in-service oxidative life. For example, one oil may have an RPVOT value of 1000 minutes, while another oil may have an RPVOT value of only 700 minutes. However, depending on actual stressing conditions and formulation factors the oil that starts with the lower RPVOT number, may oxidize at a slower rate and hence be more oxidatively stable than an oil with an initially higher RPVOT value. In other words, formulation factors (base oil and additives) respond differently to different in-service stressing conditions. In this case, the oil with the lower new oil RPVOT value may be a better choice for long-term resistance to oxidation. With that said, for turbine oils it is generally not advisable to select lubricants with RPVOT's below 600 minutes and test values above 1000 minutes are generally considered out of the range of test sensitivity.

It should be also noted that RPVOT is an excellent test for measuring the degree of oxidative degradation (i.e., additive depletion) for in-service turbine oils, by comparing the in- service oil RPVOT number to a new oil baseline.

Want more info? Here's a great article from Machinery Lubrication Magazine: "How to Select and Service Turbine Oils"

Today's Tip

• It is very important to calibrate your grease guns. Many lube techs don't know how much grease they are applying when using a particular gun. Some guns apply twice as much as others with the same single stroke of the gun. Every gun should be calibrated and labeled with the type of grease in the gun and the number of pumps per ounce (then dedicated to that grease alone).

  To calibrate, pump grease into a tablespoon until level full. Double the number of pumps (shots) and you have pumps (shots) per ounce. (Tip submitted by Mike Fitch, Temple-Inland. Thanks Mike!)

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Book Bits

From the newly revised book "Lubrication for Industry":

Color Route Systems Assist Lubrication Practices

As can be seen in the Alemite color route card, color route management systems have been in use for decades. Modern management philosophies often adopt and update these tried and tested methods. Total Production Maintenance (TPM) philosophy pays much attention to lubrication procedures and their benefits. TPM also relies on operator involvement.

This study involved a chemical process facility that was changing over to a TPM philosophy. In order to train operators to perform effective lubrication without information overload, the color identification system was proposed. All grease guns were to be standardized for output delivery and then colored for the type of grease in use.

All manual lubrication points requirements are then assessed and calculated. The points are then hooked into a manual series progressive block with a single grease nipple inlet. This block is colored according to the type of grease, and a tag plate is attached to the block engraved with the number of grease gun strokes required for the operator to perform correct lubrication.

Operators are comfortable with this method because the subjectivity of the function has disappeared. This method also encourages "ownership" of the equipment by the operator."

Click here for more information about the book "Lubrication for Industry".

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