In This Issue:

• Up Front: Why It Pays to Know Your Vendors

• Book Bits: Rolling Element Bearing Contamination

• Today's Tip: Top-up Container Best Practice

• Q & A: Screening Test for Lubricants

Up Front

Why It Pays to Know Your Vendors

We regularly test the remaining useful life of the turbine oil on our main system using the rotating pressure vessel oxidation test (RPVOT). These oil tanks hold a considerable amount of oil (85,000 liters) so any possibility of a change-out must be thoughtfully considered.

Recently, the RPVOT results came back at just 55 minutes. This sent shudders through the organization. While preparations were being made for the oil change ($200,000 + labor), we asked for a second test to confirm original results.

The second test results came back at 650 minutes and our oil- change preparations were immediately halted.

A check on the contractor showed that this company had a subcontractor who had a subcontractor to conduct the RPVOT tests. The final subcontractor did not follow standard RPVOT procedures, and the whole process had become confusing.

Asking the subcontractor for explanationshas restored our faith in this sort of test.

We learned that just because a subcontractor is an expert doesn't mean that he's above making mistakes. Therefore, check ALL the work done for you. (Submitted by Peter Reed, technical support officer, Delta Electricity. Thanks Peter!)

Let us hear from you. Each Up Front story published will earn the sender $50. Submit a case study, experience or lesson learned. Or e-mail info@noria.com.

Book Bits

Rolling Element Bearing Contamination

From "Lubrication Fundamentals".

Solid particles of any kind that are trapped between the rolling elements and raceways are the most frequent cause of shortened bearing life. Consequently, dirt should be kept out of bearings as much as possible, and lubricants should be changed before oxidation has progressed to the point where deposits begin to form. The use of oxidation-inhibited lubricants can greatly extend the period of time that lubricants may be left in service without excessive oxidation.

More information about "Lubrication Fundamentals".

Today's Tip

• We have 4 to 5 different lubricants that we use in small quantities each day. Several years ago we switched from the metal one-gallon containers to clear plastic containers. Not only are they easier to pour from but the user can see the color of the oil as they are shaded differently. Sure, we have each container properly identified, but this additional safety net has made adding the wrong lube a thing of the past. (Jim Green, Alcoa. Thanks Jim!)

Each tip published will earn the sender $25. Submit your tip.

Q & A

Screening Test for Lubricants

"What is the meaning of dielectric constant (DC) in a lubricant's performance and its monitoring? We have an instrument in our predictive maintenance department that reports these units, and we do not know how to use it." - Horacio Huallpa, Taller Motores.

There are several instruments for used oil analysis based on DC. The DC is a measure of how a material transmits electric currents, and is a simple number that is the relative ratio of the speed of an electric field in a material compared to the speed of the electric field in a vacuum.

Different materials have different DC *vacuum =1, Mineral oils =2.1 - 2.4, PAG 6.6 - 7.7, metals = infinite, etc.)

When using this instrument, it is important to first obtain the original value for DC of the new oil in order to compare it with the values of the used oil. Any change (increase) in DC from its original value is an indicator of contamination, or a change in chemistry of the oil, such as oxidation.

Other factors that can change the DC of used oil include: changes in acid number, base number, additive depletion, wrong oil, water and wear metals. The only factor that lowers the DC in the oil is fuel dilution.

These instruments are intended to screen your oil samples to monitor lubricant health and contamination. Changes in DC greater than 0.01 indicate a change in the lubricant that requires the sample to be sent to the laboratory for complete oil analysis.

Check with your instrument supplier for more information specific to the variations in technology that can affect the measuring capacities and results.

Gerardo Trujillo - Senior Technical Consultant, Noria Latin America

If we feature your question in Lube-Tips we will send you $25. Submit your question.