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How do you know when your Hyd oil has gone bad?

T tonyb 2Member
In Early Sept I posted a message regarding longevity and problems we had encountered with Shell Tellus S37.
We sample the oil at 3 month intervals, our only sign that that we had problems in the sub 3 micron area was that we were using up 3 micron Pall filter at double the normal rate, we moved to 6 micron to save filter costs.

Since then we have carried out many test on this oil to discover the problem.
Bacteria.... none found.
TAN...0.29
RPVOT.....200 mins Vs new oil of 430 mins
NAS......6
ISO 15/11
PARTICLE COUNT per 100ml 5-15 microns 2284

Viscosity is normal, and there is less than 100PPM of water.

The only other positive result we had (apart from the RPVOT)was that the oil failed the filterability test (carried out by Shell and Pall)that it was unfilterable below 3 micron.
It had a very acidic odour and was dark in colour. Last renewed in dec 2000.
Further analysis of the Pall filter media using ICP of the materials on the filter. This suggested that many of the materials found were zinc-phosphorous(sludgy deposits), which suggests depleted oil additives.

We have since emptied the oil from the tank and cleaned it, then re-filled with 23,000L of Mobil DTE Excel 46

If anybody could summarise the above and give any answers to what was really wrong with the oil, I'd be interested to hear those views.

I've also got lots of oil analysis data that I can pass on if anybody would like to see it and help us with this conclusion.
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M mrhughesMember
Tony.

I think your results looks ok. I would not (based on your data) say that there is anything wrong with it. NAS6 ISO15/11 is clean and the count pr 100 ml. in 5-15µm is very low (NAS 4) so obviously another size range classifies the sample. ANyhow new oil is normally NAS Class 7-9 (Not very clean), and Recommended for test bench is NAS Class 6.

How was the counts performed? Microscopy or Automatic?

Regarding the filterability test: Has there ever been used any form of extra additives, like anti corrosion or rust preventive? We had an experiense for a couple of years ago, when a crane offshore got clogged filters after startup. ( https://forums.noria.com/eve/forums?a=tpc&s=692608715&f=826604995&m=191105882&r=448101292#448101292 )
G greglivingstoneMember
Tony,

Your situation would certainly make a great case study!

Based on the high level of very small insoluble contaminants, strong odor and dark color I would say that your hydraulic oil has undergone thermal degradation. Thermal degradation occurs at high temperatures and produces different by-products then oxidation. Although thermal degradation does not result in an increase in acid number and the degradation by-products are smaller then what is measured by an ISO particle count, it is still possible to detect. To test my theory, I would suggest that you run FT-IR and look for a peak in the 1600 cm-1 range when overlayed on a new oil scan.

ZDDP is the most common AW additive. It is inexpensive and also acts as an oxidation inhibitor. But, it does readily form sludge. It is not surprising that you found zn/p on your filter media.

Even though you have refilled your clean reservoir with new fluid, I still suggest that you familiarize yourself with the various processes of thermal degradation. Even if your new lubricant has a higher oxidation stability, it may still be just as vulnerable to thermal degradation. I have some more information on thermal degradation, in addition to a couple of predictive tests that you may consider running. Feel free to e-mail me if you are interested: gregjlivingstone@yahoo.com
T tonyb 2Member
Hi all,
the counts were performed by microscope in all cases as we have had some bad data (as they tend to decant the sample)from companies who have used an auto process.

We have a feeling that a number of similar viscosity oil may have been put in the tank of the shell with zinc variety and that may have screwed the oil up, we have no other evidence and the zinc content of the oil is very low.

No other additives, as far as we know have entered the tank.
The tank had not been cleaned since 1987.

BTW Shell Tellus S37 was a specific product for the UK market, that Shell have now withdrawn.
T tonyb 2Member
Hi all,
Kevin... I agree, but we have no evidence...... this problem developed in approx spring this year. We have a feeling that the product arrived from Shell but may have been branded in-correctly. Our zinc content was 5mg/kg when last tested in Oct.

Just for interest the other highs were Sulphur at 2552mg/kg, Mg at 15, P at 236, Ca at 5. All others were not detected.
Water was 66 PPM.
System quantity is approx 30,000l with 23,000l in the tank, it could be only 4 or 5 drums (208l) of the "dodgy" oil product that went in to the tank, but as I said before we have no hard evidence, just a gut feeling of when these issue started, IE: something blinding the 7 off pall 3 micron filters, 6 micron worked OK.

The system runs mainly MTS Systems Corp, Instron and Servotest equipment, along with lot and lots of Moog valves and they all call for something approaching 13/09

I will also add that this time in 2000, our oil failed again (this will be the third time since 1987 that we have changed the bulk oil)... that time we had hard evidence from Shell that the oil had oxidised, it was changed for new Shell tellus S37 over the Christmas shutdown of 2000.
Last edited by tonyb 2
H hussamadeniMember
Tony,

It is a classical example of water ingress or contamination in ZDDP based Hydraulic oils.

In the presence of moisture +50 ppm, the ZDDP package hydrolises. This is manifest by the presence of whitish deposits, which invariably choke the filter media.

Many lube companies have switched from ZDDP packages. Suggest you seek clearance from lube supplier that oils are ZDDP free, or better still Zinc free type of oils.

M Hussam Adeni
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