Suitability of EP Gear Oil

[PDPumpGuy]

Can anyone help me understand why a Gear Oil with EP additives could potentially cause a a conecting rod journal bearing on a reciprocating pump to fail?

We have had repeated failures of crank pin bearings (the split, insert style, babbit lined journal bearings on the big end of a connecting rod)on a series of reciprocating triplex pumps we have in service, and the manufacturer has blamed our use of a gear lubricant with EP additives as the cause of the problem.

The oil we are using is the same viscosity as the turbine oil they now recommend, however similiar pumps from another manufacturer (National-Oilwell) actually recommend the oil we use, and I can't understand why it would work in one and not the other. Seems to me that, if anything, we would just be wasting money on an oil that we don't really need.

The bearings seem to fail by overheating, then the babbit melts away. It almost looks like they were starved of oil, but we know that was not the case. The only explanation I have heard of why EP oils should not be used with Journal bearings is that journal bearings require a thin film of oil to keep the load bearing surfaces from contacting each other. Apparently, EP oils contain sulfur, and the sulfur migrates to hot surfaces and coats them. Great for gear teeth, but bad for a journal bearing with only .002-.003" of radial clearance for oil to flow.

Seems a bit of a reach, but I would like to see if anyone out their agrees with this theory or has a better understanding of the process.

Thanks

 

[rmw]

See thread324-124116 and thread338-124133 and if you still have questions post back.

I would not that in the automotive world, transmissions (automotive gear boxes) with bronze synchronizer parts are prohibited from using EP Gear Oils, and use engine oil grade lubricants instead.

rmw

 

[bosha]

I don't think that an EP additive film would be thick or deep enough to influence clearances, or the temperatures would be hot enough to really activate it. I'm wondering if there could be some sort of compatability problems between what the manufacturer used and your EP lubricant(did they do a flush before switching). I think Chevron found that turbine fluid and motor oil add packs created some sort of insoluable calcium carboxalate to form. I'm curious why one manufacturer uses EP and the other one don't, and why would an EP be necessary.Does National Oilwell use a different bearig material.

 

[rnd2]

"..........The oil we are using is the same viscosity as the turbine oil they now recommend, however similiar pumps from another manufacturer (National-Oilwell) actually recommend the oil we use, and I can't understand why it would work in one and not the other..............."
Whatever the reason(s) it is clear the failing bearings do appear to be working harder than those used in the other brand so the choice of lubricant inevitably become crucial. If you are determined to persevere with oil that is not recommended, at least gain a better understanding of why premature failure occurs. Make direct comparisons between bearing pressures as well as lubrication arrangements of both types.

 

[PDPumpGuy]

We had decided to use the EP Gear Lube in these new pumps only to simplify our maitenance procedures (we have numerous National pumps running in our facility, and did not want to have a different process for what is essentialloy the same type of pump). Obviously we will change the oil to the MFG's recommendation to prevent more failures. We just felt that the explanation did not really seem plausible, and that's why I posted on this forum, to better understand the lube issues.

To answer another question. The bearings on the two different pumps appear to be very similiar. It's possible the clearances in the journal are a little different, or the composition of the babbit may be different, but they sure appear to be the same.

The pumps do run hot, oil temperature in the sump can reach 150F, so I expect there are small hot spots inside with temperatures even hotter. I don't know if that's enough to "activate" the EP compounds or not.

No, I don't think EP properties are necessary. There are no gears in this pump, or the National pumps, so there are really no areas of extreme, metatl to metal contact pressure.

I had also heard that the EP properties can corrode copper, so they should be avoided for bronze type bearings.

 

[turboco1]

The oil system is designed to maintain the babbitt white metal temperature below 230F. Thus the exit oil temperature from the bearing is limited to around 160F...so your sump temp of 150F is normal.

The oil may contain additives, other than the Extreme Pressure additive, such as oxidation inhibitor, rust inhibitor, detergents, viscocity index improvement agents, pour point depressants and anti-foaming agents. All additives are considered contaminants that form a beneficial surface film in one way or other.

If an EP additive is the culprit wouldn't you expect some film residue on the babbitt surface in any of the other bearings that did not fail?

EP additives are activated by temperature resulting from very high boundary pressure and not the pressure itself. With crank connecting rod pin bearings the load area is constantly moving so you would think that cooling is taking place all around in the bearing at all times nearly. Just a thought.