In This Issue:

• Today's Tip: Strobe-check While Sampling

• Book Bits: Premature Failures are Preventable

• Q & A: Fit for Service Tests

Today's Tip

Strobe-check While Sampling

• After I take my fluid sample from one of our hydraulic systems, I use a strobe light to check the coupling, because these systems are always running when samples are taken. By dialing in the RPMs of the motor, you can make the coupling appear to stop. You can then visually check the coupling for wear, cracks or damage. You can also read part numbers from coupling halves. Be aware that although they appears stopped, the coupling halves are turning at a high speed. To ensure safety, replace the guard with expanded metal or cut a small window in guard and install a plexiglass cover. (Submitted by David Lander, PdM Tech, Temple- Inland Forest Products. Thanks David!)

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Book Bits

Premature Failures are Preventable

From "Total Contamination Control"

The figure varies, but it is frequently quoted that up to 75 percent of hydraulic equipment failures are due to contamination. After more than 20 years of observing a wide range of varying product pass through repair workshops, we not only agree, but feel the figure could be higher! Sometimes the frequency of repair is so consistent and predictable that the end user regards it as the norm, when it is anything but. On other occasions, the approach to extend component life is to replace the "unreliable" product with one perceived as more "dirt tolerant" (such as replacing a piston pump with a gear pump). We believe that the majority of these failures are premature and preventable and are a result of misapplication (or lack) of filtration, and/or the human factor.

More information about the book "Total Contamination Control"

Q & A

Fit for Service Tests

"We recently experienced a massive water leak in our steam turbine. We removed most of the water using a vacuum dehydrator but I am worried we may have destroyed the oil. What tests can I perform, and what should I be looking for? We are using an ISO 68 mineral oil."

With large amounts of water, there are several problems that can occur with both the base oil and additives. For the base oil, your main concern should be excessive oxidation caused by the catalytic effects of water. To test for this, you may want to run either an acid number or FTIR oxidation test to determine to what extent the base oil has oxidized. Remember to run these two tests on both the used oil and a fresh new oil sample to allow a differential comparison of the test results.

As for additives, your main focus should be on the corrosion and oxidation inhibitors and the demulsifying additives. To test the corrosion prevention characteristics of the oil, you may want to run the ASTM rust inhibition test (ASTM D665) as well as the copper strip corrosion test (ASTM D130) to test for yellow metal corrosivity. The antioxidant additives can be tested using the RPVOT test (ASTM D2272) used to measure the oxidation stability of steam turbine oil. A low RPVOT value relative to the new oil may indicate significant antioxidant depletion.

To determine if the demulsifying additive has been appreciably destroyed, you may want to run the standard test method to determine the demulsibility characteristics of the oil (ASTM D1401), which seeks to determine how quickly the oil will shed water at elevated temperatures. Good luck!

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