We are using Mobilgear SHC XMP 320 on the gears of some of our wind turbines. But after some time the level of the Phosphorous drops significant. For some of the samples the drop is nearly 50%. I have not seen that with other gear oils. Have anyone else have the same experience? Does anyone know where these additives disappears? (I suppose filter is the most likely explanation)
Originally posted by Uffla: ... Does anyone know where these additives disappears? (I suppose filter is the most likely explanation). Best regards Uffe
Phosphorus (P)-based additives are either hydrolyzed and filtered out (especially if you have 3-micron or finer filtration system), or they are deposited on gear surfaces (which is not a bad deal as they actually work that way to form protective/sacrificial layer and therefore minimize wear). I wouldn’t worry if the concentration of P is stabilized after an initial drop and slow but gradual decrease is observed, because it is why those additives were put in the oil in a first place (predictable and acceptable process). You might want to test filter deposits for presence of P, and presence of water in oil. Also, if spectroscopic analysis show small increase in wear, it would mean that, most likely, P is where it is supposed to be (coating metal surfaces), and do what is intended/expected to do (to protect metal surfaces from excessive wear).
Posts: 233 | Location: Portland, US | Registered: Thu November 18 2004
Dear John. Thank you for the reply. The level of the water content is 50-150 ppm, and there is a very fine filter, so the hydrolyzation/filtration is certainly a possibility, just as the explanation with deposits also is possible. What troubles me is that I have never seen this drop in phosphorous level for other industrial gear oils (e.g. Meropa 320). Therefore I am insecure about how serious this problem is. If it is deposits it is most likely not a problem, as you also suggested. But if it is due to filtration the drop in phosphorous level might indicate a drop in performance. That’s why I am very interested to hear if other has some experience with this type of additive drop. I will follow your suggestion and check the deposits in the filter.
P is not a free element presence in Gear oil. It apears as complex material as Sulfurous phsphide. It is the mechanism in which SP matrial form a coating film on Gear teeth acting as as a cushion (Extrem pressure)thus preventing metal to metal abrasion. In due course of time P level would reduce as well as S level aslo because of film coating mechanism. Since BO also contains S, reducion in S level is difficult to monitor unless you know BO initial S level. The normal recommended oil change for Gear oils are 50% reduction in P level of the initial value or 50% reduction Timken OK value of the initial value. By the time P level reduce to 50%, the factors such as KV, insolubles, wear metals etc would increase. So, it is not beneficial to top up SP additive alone.
We use fine filters on our Mobil gear oils without seeing P drop. You could run a test by sampling new oil, run it through your filter system, and re-sample. That will confirm or deny that possibility. Do you use a vacuum dehydrator with these gear oils also? Or run at higher temperatures? Granted you are using the SCH but one thing I have been warned about the Mobil EP oils (based heavily on P and S) are prone to damage due to the heat during the vacuum dehydration process. This could be true for other EP products but Mobil is what I am most familiar with. Might be a correlation between the products.
Just some thoughts. Let us know what you find out.
This message has been edited. Last edited by: remmious,
All good advice but have you checked that perhaps the wrong oil has been added or is the problem the same oil same gear box with the Phos dropping over time? If so id say additive drop out due to oxidation, filters, water or sample/lab error. bruce CLS
Posts: 153 | Location: SF Bay Area | Registered: Fri July 15 2005
Bruce, thanks for pointing out the obvious that we all missed and it's probably the most common mistake. It should be easy to find out if it's being diluted with the wrong oil so I would check that first.
Top-up with the wrong oil was also my first thought. I actually made this comment on some of the analysis until I realize that the drop was a tendency for samples from different country's and locations. I then investigated this issue further and today I am completely sure that the drop is not due to wrong top-up.
This term, "WRONG OIL", got tossed around too often without any elaboration. In my opinion, the term doesn't mean much if one chose not to be a bit more specific. Are the additives incompatibility an issue, or incompatibility of base oils, or solvency, or different grade (viscosity) of the added lubricant, or additives are inadequate (wrong kind, or too much, or too little), or what? And how to find out there was a "wrong oil" added (which testing methods to run or what)? No offence intended, but there are many folks out there that might have a hard time handling this dry term of “wrong oil” in their quest to find the right remedy for their problems. Agree? Or disagree?
Posts: 233 | Location: Portland, US | Registered: Thu November 18 2004
