TAN of used rotary screw air compressor oil

Dear,

The limits for TAN should be set upon how much TAN the fresh oil has...The limit is normally from 1 to 1.5 but can depend upon the oil.You can set up your own standards upon the type of oil and its application.

Hope this helps

Cheers

thanks for reply.
i know the new oil TAN,but i wanna know the acceptable increase of it in operation.foe example for an "atlas copco" rotart air compressor?

i understand that the fresh oil tan of this oil can be around 0.25.....so the above said range can be used.

Better informed may help this friend out..


Cheers

it is an Iso VG 68 oil with TAN of about 0.3 .after some month in operation the TAN reached about 0.65.i wanna know if this increase is ok or not?the trend shows no sudden increase,

I've not come across a TAN limit set by Atlas Copco for rotary screw compressor, only for centrifugal compressors typically running a turbine oil, the maximum for this is set at <2.0 for aged new oil after 1000hrs (ASTM D943).

As you have a rotary screw compressor - are you using a synthetic compressor oil? Typically, the oil change period for synthetic PAO based compressor oil ranges from 4000 to 8000 hrs depending on the severity and temperature of the application.

excuse me for my mistake in typing.we have some screw air compressors,we use mineral oil with TAN of about 0.3

Mineral compressor oils are changed out frequently around 2000 hrs or less typically. The TAN can be measured and trended. It is normal for the TAN to increase gradually over a period of time. I am not sure what the cut off limit would be to change the oil out as it is different from compressor to compressor. This is because varnish can sometimes build up in the oil even when the TAN is low. As screw compressors run fairly hot, I'd suggest to get a colour test done with the lab (ASTMD1500) compare it against the new oil. Perhaps a varnishing index potential as well.

I'm not sure the D 943 reference will be much use in field operation. D 943 is a product development test. That NN/TAN/AN (whatever it's fashionable to call it these days) is the measurement of the oil after ~12 weeks (2000 hours) on test in a bath at 93C with some DI water and an Fe/Cu catalyst coil with O2 bubbling through (flow rate escapes me just now).
If you want to be ultra-careful, a limit of 0.5 mg KOH/g above the fresh oil result is the most restrictive limit I've heard.
The fact that the equipment manufacturer has not set a used oil TAN limit indicates that TAN may not be the useful indicator for this application.

Would it make sense to have some form of on-line oil condition monitoring in this application? There are sensors which will give remaining oil lifetime, and oil condition availabe - this would allow users to set their alarm limits and give them better control. What do you think? Is it applicable for this type of machinery?

quote:

not sure the

which parameters set the alarm for oil life?

Hi Laleh,

TAN AN NN results only is not enough to predict the lubricant and plant condition.
You should be also considering Oxidation, particle count, PQ and last the trends in wear metals and additive levels via spectrographic analysis, if TAN Oxidation, particle count, PQ and wear metals were all trending up and additives trending down then action would be required, we would check by microscope what the debris is and decide best maintenace step from there, TAN can trend up 2 numbers and the lubricant still be acceptable but as the TAN shifts so does vanish potential re Rene's recommendation for the ASTM D1500 colour test.
TAN on it own is not enough to decide lubricant and machine condition but with the others tests a valuable part of the info required.


regards


Rob S


rttech.com.au

Laleh,

you can go to:
ASTM D 6224, it is standard practice for monitoring In-Service lubricating oil. Alarm limit is also stated there for some of general application.

ASTM D 4378, more specific to monitor In-Service Turbine Oil

Every equipment, operation and environment is unique. Just discuss with Technical Support of your oil vendor.

regards,