The oil in our main lube oil reservoir is Mobil DTE797. All samples of new oil have consitently had Phosphorus content in the range 1 - 3 ppm (12 samples spread over more than 10 years). When in the sump, it consistently has phosphorus range 15 - 30 ppm (bounces randomly up an down within this range). The sump is 20,000 gallons.

Oil was drained and refilled (due to degrading oxidation characteristics) and the reservoir immediately jumped to it's former range 5 - 30ppm.

We have two of these 20,000 gallons sumps. The same scenario occurred on both. (15-30ppm phosphorus both before and after their respective oil changeouts)

All samples (in the reservoir and new oil) are done by the same lab, with metal (phosphorus) content determined by ICP.

Can you explain it? Where did the relatively large amount of phosphorus come from when the oil was changed if it wasn't in the new oil?

ePete,

I remember reading somewhere, with the presence of moisture (beyond a certain ppm), ZDDP will hydrolize and result in whitish deposit (Phosphorous) on filter media and cause clogging. In line with that, could your phosphorous escalation in the sump be related to moisture ingress during oil change; I see a good possibility of this happening.

Cheers....Rajan Muthukrishnan

What does the lube oil reservoir service?

Are there any phosphor bronze components coming into contact with the lube oil?

What is the whole lube oil circuit? Does the lube oil flow through some components which contain phosporus?

Thanks for the comments. We have an open mind on this one.

These are the main lube oil systems for large steam turbines It has oil pumps and services the bearings. I'm not sure about phosphorus/phosphrus bronze components – certainly possible.

The thing that strikes me is that the concentration of phosphorus appears to jump between the time when it is sampled new and when it is sampled in the reservoir. And once in the reservoir, it doesn't continue to increase.

And let's look at how much phorsphorus is represented by an increase from 2 ppm to 17 ppm (a 15ppm increase):

The ppm represents a weight fraction. The total weight of the 20,000 gallons of oil I think would be in the range of 128,000 lbm. An increase of 15ppm would be 15E-6 * 128,000 = 1.92 lbm of pure phosphorus. That sounds like a lot to me.

I wonder if there might be some way that the phosphorus was present in the new oil initially but in a form that doesn't show up in the ICP test. Then there is some reaction or change that takes place when we transfer it to the reservoir that puts the phosphorus into a form where the ICP test can see it. It might be similar to the hydrolisis mentioned above. It would have to be a very rapid process.

ePete,

Is there a heat exchanger in the lubrication circuit? Off the wall, one possible point of phosphorus contamination is from some coolants.

Normally, turbine oil has no antiwear additives, so the 1-3 ppm phosphorus levels could be residual from the base oil. Those levels are within the repeatability levels of the tests.

It is possible that there is free phosphorus in the oil in sizes greater than 10 microns which might break down in the presence of water and produce smaller particles that could be picked up by ICP. If you still have a sample of the fresh oil, running an FTIR on the fresh oil and the sump oil would show any increases in phosphorus content (regardless of size) in the high frequency end of the spectrum. Let the lab know the specific reason for the test so they can look at the right area.

Ken Culverson

Attached are some trends. All on the same scale. You can see new oil is much lower than U1 (unit 1) and U2 (unit 2). Both units had the whole sump changed since 2005 - I am not sure the exact date - will try to get that info and label it on the chart.

Leak of cooling water seems like it would bring other contaminants. Water to start with. But also I think sodium hypochlorite is at a large concentration in our cooling water.

I tend to think like you suggested that particle size or some other attribute makes it nondetectable to the ICP in new oil but shows up later. I'm not that familiar with FTIR (can it show a concentration?). Seems like a great avenue to investigate. Come to think of it, our oil lab is one resource we haven't tapped yet so we'll have to ask about this and other tests that might shed some light. Thanks for the suggestions.

phosphorussmall.ppt (264 Kb, 6 downloads)

Sound like it's the new oil problem. Have you contacted your oil supplier? They should know their oil characteristics fully whether it's emulsifying or chemical raction etc....

Has the oil brand or specs changed in the 2005 whole sump change?