Five years ago, Dr. Tim Nadasdi, a senior chemist with ExxonMobil, did a survey of several hundred in-service samples and sent them to different labs using different technologies to measure the particle count in the oil. The standards were previously just for new oils, said Gerald Munson, of Fluid Assets. Nadasdi decided to focus on ASTM D-7647.
Munson, who is a member of the ASTM Committee D02 on Petroleum Products and Lubricants, said Nadasdi found that depending on what technology they were using, they received variations, as much as +/-4 ISO codes in the particle counts on identical sampling.
“This is disturbing to him. He was the one who started the search for a method that would make that difference much smaller, much more repeatable, much more reliable than it had been in the past, because there was no standard on how to use those automatic particle counters, to look at in-service oil,” Munson said.
“The standards previously were just for new oils. This standard comes up with a method that removes almost all of that variability through dilution. The sample is diluted, 50/50, with a solvent which can take care of air bubbles, water particles and take care of the influence of soft particles in the oil.
“By doing that, you’re only measuring the hard particles in the oil and those are now measured accurately, repeatedly and reliably with the laser automatic particle counter, which is commercially available.”
This new variation talks about all of the different influences that it can take care of, but also what are the interferences that can still give the method problems, how to prepare the apparatus, how to prepare the collection and handling of the sample; all of the formulas for the change in the viscosity, Munson said.
“Turns out with the solvents we’re using, almost regardless how heavy your sample is, it can be a very viscous sample or very light. These procedures normalize it right around an ISO 15 weight, which is very easy for these automatic particle counters to pump it through.” Munson said.
“You have to have a constant steady velocity that is known through these automatic particle counters, or it creates an error. It’s a very simple, straight-forward procedure.”
Munson said ASTM members are attempting to show the proposal to various testing agencies around the world.
“We’re going to be going out, proposing this to a number of laboratories that routinely do this, to get away from the influences that we have from water, air and soft particles in the oil. Soft particles can also be sludge and varnish.” He said.
Munson said that for different particle sizes, there’s a different reproducibility. It’s just inherent in the methodology. This is only one dilutant, but there are four separate dilutants to be used for different reasons in the method. There is only the one precision statement for now.
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