We are operating the Power Plant 2 x 610 MW.Currently we have problem of low RBOT values. Initial value was 633 minutes in 1998, and now is 229 minutes (2005). The TAN value increase as well from 0.2 to 0.4.
We use EP 46 oil and top up using XEP 46 due EP 46 no longer in production. we plan to change out the oil in the following outage/shutdown, but is that necessary? Is anybody having experience? arief.saptahadi@ytljt.com

Do you have more than just 1998 and 2005 RBOT (now called RPVOT)numbers. If you did, you could look at trend - steady state due to top-offs versus linear/acclerating depletion? What are RBOT values of EP and XEP oils? Have you had patch test run to look for sludge build-up, varnish potential? Are antioxidant additives in EP (phenols) and XEP (?) the same? You have to be careful interpreting RBOT values when mixing oils. There was an ASTM symposium on Turbine oxidation monitoring in early December 2005 - not sure when presented papers will be available on ASTM website.

Hi Bob,
Thanks for your reply.
The last RPVOT (ASTMD2272)of mixed EP-XEP was 226 minutes is in service since 1999.
Initial RPVOT of EP was 633 minutes.
The initial RPVOT of XEP was 1179 minutes.
The initial mixed EP-XEP (25%-75%) was 586 minutes.
The last TAN number was 0.39 while the initial was 0.15.
There is no phenol antioxidant additive left in oil as per RULES test.
With this figure, shall I propose to boss to change out oil?

Keep in touch.

What is/was the TAN of the new XEP/EP-XEP mixture? Many of the newer additive formulations are acidic and could account for the increase in TAN instead of oxidation.
Seems strange that the RPVOT of the mixture is lower than EP, would expect closer to 1000 minutes than 586. Did anything -such as additives fall out of the mixture? Different basestocks such as Group 1 (EP) vs Group 2(XEP)?
Is there any amine antioxidants in the XEP or used oil?
How long ago did you run the RPVOT?

Hi Bob,

The new mixture EP/XEP TAN is 0.18.It is an amine additive in the oil. It is 38.8% remaining in the used oil. We run RPVOT since April 2005. We take samples every quarter. How low can we go for RPVOT? 25% from initial oil or initial mixtured oil? or How far can we go for TAN? 0.4%?
We have discussion with the Oil Rep. They suggested nothing.

Sorry, this information was left.
There is no phenol antioxidants left in the oil. We do not know the the base stock group. The Oil Rep mentioned that both product is group #2.
Currently the Turbine OEM keep pressure on us to change out the oil. But we still try to find out why the oil prematurely fail.

If I understand correctly, your last RPVOT was in April 2005. You take samples quarterly. So you took samples March 2005 (April RPVOT), June 2005, September 2005 and January 2006? What data do you collect on quarterly samples? (TAN, RULER, sludge, etc.?) Any trends such as TAN increasing?
I don't have the knowledge or experience to tell you whether an oil change/recondition/no action is the best course to take. So for what its worth, my recommendation would be to have another RPVOT performed on current used oil and on new oil mixture (confirm mixture is below either new oil). Have you been topping off with XEP oil so oil in turbine now >75%XEP? Have sludge measurement/varnish potential made on used oil.
Then use ASTM D4378, Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines to help you/support you in making your action. Normally 25% RPVOT is an action level, problem is the RPVOT for your mixture was lower than either oil making the 25% value uncertain.
How much life were you expecting from oil? What data is turbine manufacturer using to support oil change?

This message has been edited. Last edited by: Bob K.,

Your problem is in the mixing of oils. Noria has a chart showing the erratic RPVOT reponse to oil mixtures, versus pure oils, even when the mixtures are of the same basestock Group.

Send me your email address and I'll send you the chart

Lubecheck@focuslab.co.th

Well folks, there is a third and very logical conection to low RPVOT and elevated AN, and somehow got not mentioned. It is a trace metals analysis. We all agree, don't we, that acid causes corrosion. Well, if I would be concern with high AN I would check and track spectroscopic analysis, and see concentrations and their trend. But in your case, I thing you your oil is slowly approaching the end of its service life. You can get by for a while with the "sweetening" technique (because that's what you've been doing), but tell you boss that you should start making plans to replace your oil.