Bent Impeller Blades. What happened? 5

[Wes-in-WV]

641 HP centrifugal air compressor, 3045 ICFM design flow, 100 psig discharge to a common header (probably 1 other identical machine running at the time). High vibration alarm leads to disassembly and the discovery of bent impeller blades. I'm not sure what could have lead to this sort of damage. Any ideas?

 

[LittleInch]

A rock, stone, animal, bit of wood.

Pretty brutal damage.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Wes-in-WV]

It has a screen and filter on the intake. At least it used to. Maybe I should go look to see if it got sucked through. It's a weird sort of damage though. It looks like it was run backwards with a softball inside. I'm at a loss.

 

[Wes-in-WV]

Might be off on the run backwards part.

 

[LittleInch]

A bit of one photo doesn't give anyone much to go on. Is the shaft horizontal or vertical.

Surely someone knows if the screen was missing.

641HP is a bit of a beast alright.

Have you dismantled it yet? More photos.
What should it look like?
You need to give us a bit more.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pmover]

any possibility of cool-to-cold humid air entering the system & drop in pressure where moisture froze somewhere and then suddenly breaks off and strikes the impeller blades?

had this happen to a gas turbine, 1st stage in compressor. the only damage was 1 blade bent, but all the bearings in accessory gearbox were damaged by the acoustical noise created by this flat blade. a strange situation . . .

 

[georgeverghese]

Looks like the compressor shaft is bent too - motor to compressor bull gear coupling misalignment or gearbox failure?

 

[Wes-in-WV]

I'm not able to get any better photos at this time. I agree there's not a lot to go off of. I was looking for spitball answers and you guys delivered, thank you.

This is a horizontal shaft and I believe it's the second of two stages. There's an intercooler between stages, so I guess a possibility of water, but I don't think there's any refrigeration that would get it cold enough to form ice.

I'll report back when I get more info/torn down further.

 

[LittleInch]

Looking at the blades underneath this must rotate counter clockwise normally?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Wes-in-WV]

That's what I was told by a more experienced colleague. I had assumed clockwise when first looking at, but that's probably because I don't know an impeller from my elbow.

 

[JJPellin]

I have seen similar damage many times. One was certainly hit with a slug of liquid. One touched off a rub when the pinion thrust in reverse as a result of running with low downstream pressure. One rubbed hard on salts built up on the head as a result of changes in process chemistry. For an air machine, water is the most likely explanation.

Johnny Pellin

 

[georgeverghese]

Upstream intercooler flooding due to liquid drainer failure may be a suspect cause if there was a rise in the suction temp to this stage.

 

[compguy22]

How is the other stage damage if any? given that there are two stages only and assuming intercooling, this looks like titanium or special alloy made impellers for semi-open type are required to reach what should be around 440 m/s peripheral tip speeds with the high speed shaft spinning at 60000 rpm or so if we assume around 150 mm impeller outlet diameter.

- If not titanium or special alloy, I am not sure how excessive stress on semi open impellers can be coped with at those operating speeds. Is this is 1st time running machine ? if not, how long has the machine been running? did the failure occur during start up (high axial load)?
- At these speeds and power density, minor unbalance, misalignment, bearing issues and component fatigue (for instance due to partial loading or cycling) can lead to catastrophic failure.
- Absence of proper surge protection can also be a cause for failure.
- Manufacturer failure to do a proper modal study of the impeller may lead to impeller vanes fatigue and failure.
- In addition to above, there is possibility of ingestion of foreign object as already mentioned.

I am bit surprised with the overhung mounting of the impeller onto the shaft as this does not look like a high quality/precision manufacturing? There is no ogive at the impeller inlet. What is the brand name? is this designed to API?