Rotation of turboexpander with no lubrication 1

[Iradah]

Hello all,
We have a turbo expander of a maximum speed of 18500 rpm. We S/D the unit for some work. The inlet XV was passing and the unit was running at 2000 rpm with no Lube Oil for ~ 8 hrs.
What do you think is the consequence of this rotation with no lubrication? We currently are facing vibration issues.

 

[JJPellin]

It is almost certain that the bearings have sustained serious damage. If you want more specific comments, you need to provide details about the bearing design, rotor weight, continuous monitoring and the nature of the vibration you are seeing.

Johnny Pellin

 

[MikeHalloran]

The normal operating speed suggests that the turboexpander is equipped with plain (not plane) bearings.

Plain bearings at 2000 rpm for 8 hours with no lube oil have probably disappeared completely.

It's time to unpack your spare turboexpander. ... or go get one.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

Whether the bearings in your turboexpander are journal or rolling element, they will have likely sustained some amount of damage from running at the speed & duration noted with no lubricant flow. Besides scuffing/scoring damage to the radial bearings, there may also be damage to the thrust bearings and seal faces.

As MikeHalloran said, the prudent course of action would be to replace your turboexpander and clean the lube circuit thoroughly. Hopefully you can use the downtime to evaluate changes to your existing system layout and operating procedures so that a similar event does not occur in the future.

Good luck to you.
Terry

 

[Iradah]

Thank you all for your input.

currently we are running the turboexpander at 11000 rpm. it was running at 14500 rpm and operations reduced it further to 11000 rpm after getting more vibration indication.
Operations will wait unitl an external support comes and anlayzes the situation before taking the unit out, I have a real concern of more damage under current situation.
currently maybe the bearings are only damaged and the shaft is still Ok.
at this current moment, operations are trying to increase the speed again to 14500 rpm.

What do you suggest as an immediate action?

I have copied the following from the manual, hope it clarifies the type of the bearings.
((The radial bearings used on this order are tilting-pad bearings. They are five-pad, load-on-pad,
nonadjustable bearings especially designed for the high speeds demanded by turboexpander applications.
Thrust bearings are a fixed tapered land type thrust bearing that is integrally machined with
each journal bearing.))

 

[tbuelna]

I would suggest that you stop operating the unit. The damage it has sustained so far does not sound too bad. But if you continue to operate the unit, it may experience a more catastrophic dynamic failure due to seizure of the bearings or contact between the turbine wheel and housing.

One possible method to determine which components suffered damage would be to take a sample of the lube oil and send it out for analysis. This will tell you which kinds of metals are present in the oil, and based on this information you can draw some conclusions about which components were damaged.

Good luck to you.
Terry

 

[Iradah]

Thank you tbuelna.

operations intend to continue running with the unit for at least 5 days more until the rotating equipment engineer arrives.

Please let me know how much risky is this decision.

 

[LittleInch]

In the words of Clint Eastwood - "Do you feel lucky??"

You have a unit which for understandable reasons is showing signs of great distress and you still keep running it. There are few hard bits of data here to say how badly damaged it is, but if you can check the oil or even look inside the sump or the filter and extract bits of the bearing which have already been flushed away, you may be able to get some hard data.

I don't know your position in this company or your reporting lines of responsibility, but if I was you I would place your concerns on record in writing (e-mail or report), to your superior (kepeing a copy safe somewhere), making the point that every day of continued running creates ever greater risk of catastrophic failure, so not just 5 days, but more like 5 months of the loss of your turbo expander and let him or her make the call.

Why is it taking so long for a rotating machinery specialst to arrive??

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Iradah]

LittleInch, I expected this reply.
I am a process engineer. The rotating equipment engineer, the plant team leader and the turbine tech are off. There is no specialist on this area until next week. Although I look after process support in the plant and not responsible for vibration analysis, I feel it is my responsibility in some sence to try to know if I need to raise the concern of running the unit until next week, I am worried about more damage to the unit.
Please let me know more about how easy it is to check the lube oil filter for metallic parts while the unit is running, I need to be very clear on this for operations to take the action and do it.
I have attached some data collected for the vibration. Can you help me interpreting the data please. Thank you.

 

[MikeHalloran]

Just exactly how dire an emergency does it take to get someone to interrupt their normal schedule and get on a redeye?

No matter; you'll have one that's big enough, real soon, I expect.

I hope I'm wrong.


Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

Operation of a bearing that requires lubrication without any lubrication is bad.
Operation of high-speed rotating machines with vibration is bad.
Operation of high-speed rotating machines with damaged bearings is bad.

The job of "operations" is is to operate the plant to produce product and make money. Stopping equipment is not something they will do on their own - ever.

When the turbo-expander explodes "operations" will say "engineering knew about the issue, but engineering did not tell us that we had to stop running it".

Since you will likely soon be looking for a new job, you might be interested to note that there is a jobs link on the left side of this site.

 

[LittleInch]

Ok, a little flippant, but I think you have written the first part of your e mail to whoever is left in charge,

I am a process engineer. The rotating equipment engineer, the plant team leader and the turbine tech are off. There is no specialist on this area until next week. Although I look after process support in the plant and not responsible for vibration analysis, I feel it is my responsibility

Then add "to advise you that the machine is vibrating after being accidentally spun for 8 hours without lubrication and I believe it has a significant risk of damage or destruction. I am not able to judge how badly damaged the turbo expander is and request urgent support."

Then make sure you attach the files you sent us and don't go any where near the thing. You've done the best you can and others need to take the responsibility to turn it off and fix it or keep it running. At least you can say you told them. Sometimes that's all you can do.

Good luck.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[tbuelna]

Iradah-

If your data acquisition is showing vibration levels or shaft displacements outside of limits prescribed by the OEM, then that should give you all the justification needed to pull the unit off-line.

Right now you likely just have damage to the spool assy (shaft, seals, bearings, etc), but continued operation could result in damage to other components. For example, there is very little clearance between the turbine/compressor wheel tips and the inner housing surfaces. If the radial shaft excursion becomes excessive due to bearing wear, the turbine/compressor wheel tips could contact the inner housing surface which would produce a catastrophic failure. These machines are designed to safely contain these kinds of energetic failures, but the relative cost to repair the unit after this type of failure would be quite substantial.

Best of luck to you.
Terry

 

[Iradah]

Operations are still running the unit, they cannot think of bearing damage as they all agree that no way for the unit to run if the bearings are damaged.
The lube oil filter is very clean and no parts of the bearings.
the vibration is showing less than 0.6 but then suddenly starts to vibrate more during night and the unit trips. we noticed that the viscosity of the oil is dropping in less than 24 hrs by 20 cs, this will lead to vibration. we are investigating possible reasons of oil contamination.
the last 24 hrs, the unit is running stable at 14500 rpm with no trip, hope it will not trip tonight. so it does not seem as a bearing damage.

the question is how can the unit run at 2000 rpm for 8 hrs with no damage at all?
if there is a damage, then where is it??
do we need to stop the unit if it showing currently stable performance??

 

[LittleInch]

Would parts of the bearing end up in the filter or just drop to the bottom of the sump?

Maybe you got lucky.

However I doubt you have got that lucky that you don't need to stop the unit and look at or just replace the bearings.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MikeHalloran]

We have all seen reports of two-stroke outboard motors running on straight gasoline for tens of hours, nominally with no lubrication. Of course, the oil quantity present is not zero, it just gets progressively diluted. ... and nobody asserts that the engine is undamaged, just that it keeps on running, and may even have a usable life after the hurricane/ flood/ whatever, when lube oil becomes available again.

Similarly, sort of, your turbomachine has tilting pad journal bearings that were probably quite nicely machined of a nice soft alloy. They are probably a bit less thick now than they used to be, and possibly scored.

Tripping on vibration means the machine is trying to tell you that it's been hurt, and needs triage.

At least caution the production experts to not loiter in the plane of the turbine proper. I'm assuming that it's not equipped with a full competition scattershield.





Mike Halloran
Pembroke Pines, FL, USA