Oil discoloration & high bearing temperature 1

[Mahmoud Bassiouny]

We are struggling with many pumps that oil discolored with brass particles at overhung pumps with 3600 rpm speed
Elemental analysis declared that oil rings ( Bronze)are the main reason for these oil discoloration, and when we opened the inspections plugs at bearing housing NDE we observed 2 oil rings out of four are not rotating smoothly and the remains two rings are running erratically,ISO VG 68 oil
We are discussing to a non-metallic oil rings, does anyone has an experience of using these non-metallic oil rings? And what is the recommended material to be used?

 

[dik]

How is it discoloured? What is the appearance?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TugboatEng]

Here is an article about oil rings. It does mention better performance with plastics. It also alludes to your oil viscosity being too high. Overall, oil ring is a poor option.

https://www.machinerylubrication.com/Read/28378/oil-rings-lube-delivery-mechanism

 

[dik]

Thanks tug... good article.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Mahmoud Bassiouny]

Thanks “dik”, Oil turns to black color

 

[Mahmoud Bassiouny]

Thanks tug, is there any standard or OEM supports the plastic oil rings? And what is the material specification to avoid chemical reaction with oil?

 

[electricpete]

Yup, we have 3600rpm overhung pumps with same problem. Dark oil, sometimes migrates up into oiler bulb. Samples show high brass. We do a lot of oil changes. Sometimes inspections shows the oil rings are thinner than new (lost of a lot of brass) so we replace them.

Inspection of the oil ring through a viewing port or vent port might allow you to "catch it in the act" of oil ring jumping around. We see it come and go on our vibration surveys. I'm not sure any of that teaches you anything useful though.

We've actually been living with it for a long time. It hasn't caused any reliability problems, maybe we're just lucky. I've heard our pump guy talk about some options but never got anything across the finish line. I gather each option had some downsides. The one that got closest got called off because they figured out it would be too difficult to install the ring they wanted into the pump.

One thing that strikes me, pump OEM would be an important person to talk to in order to get their perspective before doing anything. If you're lucky they have already helped someone solve this problem on similar pumps.

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(2B)+(2B)' ?

 

[TugboatEng]

If you want to try plastic, I would give polyamide 46 aka Stanyl a look.

A fitted slinger ring may be a better choice.

 

[JJPellin]

We started using non-metallic oil rings as our standard in all pumps about 10 years ago. This is the standard for most of the pumps manufactured by Sulzer. We buy some of the rings pre-manufactured and make some of them in our machine shop. We use LuyTex and have had great results. In a very small number of pumps, the non-metallic ring is unstable if made to the same dimensions as the brass ring. For those, we usually just make them a little bit thicker and that settles them down. We probably have these running in over 1500 centrifugal pumps of many different configurations. Our standard oil for overhung pumps with ball bearings is an ISO 46. We use ISO 68 in some very hot service pumps.

Johnny Pellin

 

[Mahmoud Bassiouny]

Thanks JJpellin, which LuyTex grade you are using C3xx? It worth to highlight that we are facing this issue ( black oil) at hot pumps ( operating temperature) 350 deg.C with ISO 68 oil

 

[TugboatEng]

The bearing can't be operating at 350C. That must be the process temperature. What is the oil temperature?

 

[Mahmoud Bassiouny]

Yes process temperature is 350 degC, bearing temperature is around 70 C and during summer it teaches to 90 C

 

[TugboatEng]

In the article it mentions ISO 46 being the ideal viscosity for oil rings but your application requires ISO 68 due to temperature. Has any consideration been placed on using an ISO 46 oil with a higher viscosity index? Generally, when running "synthetic" oils a one step reduction in viscosity provides the same wear protection as the higher viscosity mineral oil. A synthetic ISO 46 oil may be worth a try.

 

[JJPellin]

We use LuyTex C321 for our non-metallic wear rings. I agree that a full synthetic ISO 46 is a good choice. I did not mention that we use a full synthetic ISO 46 as our standard oil for this type of application.

Johnny Pellin

 

[Mahmoud Bassiouny]

Did you observe any change in bearing temperature after using the non-metallic oil rings?

 

[JJPellin]

I am not aware of any change in bearing temperature. But, keep in mind that brass particles in oil act like a catalyst and accelerate oxidation. The oil does not have to be excessively hot in order to oxidize. If the brass oil rings are unstable and are brushing up against some surface, wearing off brass particles in to the oil, the oil will turn black, even if the temperature is normal. I think we see better oil delivery with the non-metallic rings. I believe we have better oil life because of the removal of one source of brass in the oil. And, I believe that all of this results in longer bearing life.

Johnny Pellin