OIL ANALYSIS, CAN YOU ANSWER THIS QUESTION PLEASE ?

Rowan,
First - The difference is concentration of wear metals is negligent, and should not be considered as a factor in an attempt to clarify the difference of the ISO cleanliness readouts.
Second - I see four possible reasons for differences in ISO codes:
1. Ingression of dust and/or dirt. It could happen through vent and/or cover, or by adding un-cleaned new or makeup oil.
2. Inadequate cleaning of sampling port and/or inadequate flushing prior the sampling could be a reason for seeing more contaminants.
3. Sample bottles not being equally filled. If first sample bottle was filled up to the “zilch” thus not allowing proper agitation of sample in the lab prior analysis, it would show oil to be cleaned than what it is. Bottles should never be filled more than 50-75% of its volume.
4. There are “real” people working in labs, and could make mistake as many of us do.
a). The instrument calibration may have been “out of whack”
b). Cross contamination may have occurred if instrument was not rinsed sufficiently enough from previously analyzed highly contaminated sample
c). Inability to homogenize sample prior analysis due to sample bottle being overfilled
d). Mistakenly analyzed, recorded, and reported wrong (someone else’s) sample.

My suggestion is: resample and reanalyze particle count, or call the lab and request reanalysis of both samples. These analyses are very cheap to run, and they should still have both samples on hand.

Rowan,

The Ca, Mg & Zn would be part of the additive package used in the makeup of the oil, it appears to be a zinc antiwear hydraulic oil. It's best to check a new oil to determine the additive levels. There will also be slight differences in the add pack level due to the different batches which may explain the difference you are seeing. The difference in the ISO count may be due to the particle counter - if it is an APC or lazer particle counter - air bubbles present in the sample are seen & counted as particles so sample preparation is very important. There is also what is known as additive interference. Some additives are dispersed into the oil as opposed to dissolved in the oil for example silicone antifoam - could range from 3 to 8 microns dispersed in the oil. This range is within the >4um & >6um size. It may be why you are seeing the difference in the ISO codes. Some labs offer ISO cleanliness via a 'filterpatch' test ie the sample is washed with clean solvent and filtered through a 1 or 3 micron filter. The filter viewed under a microscope and compared to a comparator eg PALL comparator to determine the ISO cleanliness codes. The ISO cleanliness codes obtained via this method tends to have very little difference from operator to operator & lab to lab.

quote:

Originally posted by ReneWA:
Rowan,

...There is also what is known as additive interference. Some additives are dispersed into the oil as opposed to dissolved in the oil for example silicone antifoam - could range from 3 to 8 microns dispersed in the oil...

Rowan,
All antifoam additive particles in any hydraulic or turbine oil are way smaller than 1-micron in size. Otherwise, 3-micron off-line filters, which are widely and successfully used in the industry, would regularly skim out de-foamants. Please check you references. The bottom line is – whatever is filtered out by 3-micron filter, it should not have been in the oil in the first place. The only filter size limits should be considered with heavily additized oils such as gear oils, motor oils, EP-fortified oils containing solid additives (platelets) and similar lubes.

John,

The size of silicon antifoam has been determined through SEM EDS on new oils. It was found to be less than 10um regardless of manufacturer. So the plant and blend process does influence the size of antifoam. The filters do not necessarily filter out all the silicone antifoam as it still is an organic molecule that can weave it's way through the filter media dependent on the media.

Rowan,

CAT have an excellent publication on managing fluid cleanliness which explains additive interference issues in detail. It's publication SEBF 1020 April 2006 Managing Fluid Cleanliness. You will find it interesting reading. It goes further to explain sample pretreatment prior to running the sample through an APC. Not all additives causes interference but if it is suspected, then get a filterpatch test done and get it viewed under a microscope to determine what is causing the increase in ISO.

Rowan,
A couple of questions first: Where are your sampling ports located, how long was the machine operating when each of the samples were taken, Was the fluid topped off or any maintenance done on the system between samples? The answers to these could explain the difference in contamination. If the sampling port is in an elbow or an area that will allow the settling of contaminants, that could account for the code differences. If the machine was not at temp during one sample or had not been running, you can get differences in ISO codes. Topping off the fluid can also change your code. If you topped off the fluid in the tank and did not filter the fluid properly, you could be introducing fluid with a higher contamination code than what is in the tank. Finally, if any maintenance was done on the system, you could have introduced contamination into the tank. For more info on the oil analysis I would suggest the book "Oil Analysis Basics" It can be purchased from the online book store. It is very good in explaining how to take samples, what some of the drawbacks are, and what the testing and analysis means. Hope this helps.

Both cleanliness results are pretty clean, our experience has been that cleanliness can be affected by -

Dirt ingress while sampling (even from air from the plant atmosphere).
Whether the machine is running at different temp or been under any load, stir up particles.
lab technique - how vigorously the sample is shaken or degassed in the sonic bath.