Turbo Failure

[Danandersen]

Hi Guys,

I know I don't post often, but I really appreciate everyone's effort to help others.

I ran into a problem with my Turbo the other day - the bearing just snapped right off.

Does anyone have any idea why that would be?

 

[VEBill]

Not my area of expertise, but might it be the old issue of turning off the oil pressure (engine off) while the turbo is still whizzing around at 100,000 rpm?

Stand by for others.

 

[turbomotor]

Do you have pics of the bearing and/or the shaft? The cleaned up and sectioned center housing doesn't lend any clue to exactly what happened.

 

[Danandersen]

Turbomotor,

These are the only pictures I have - the bearing looks like it just broke right off - could not see any discoloring on the bearing, I dont know about the shaft.

My theory is the bearing broke off causing the damage you see in the pictures.

 

[Danandersen]

By the way - notice the rubbing marks on the trailing edgedes and the ~ 1/4" crack on the blade on the compressor wheel and the
missing blade on the turbine wheel. I did recover part of the missing blade.

 

[enginesrus]

I can't see the bearing. Just see a leaky mess, bad seal.

 

[SwinnyGG]

The bearing broke off, made it magically through the turbine, and caused FOD?

Looks to me like you experienced a thrust bearing failure and contact between the rotating assembly and its housings. What do the inside of the turbine and compressor housings look like?

You can't know that 'the bearing snapped off' until you take the center section apart.

 

[LionelHutz]

Generally bearings don't just snap off. The shaft can snap off inside a bearing though but I don't see any proof this happened either.

Did the bearing actually just fail, as in the rollers fell out?

 

[durablack2]

Turbo surge can cause this on the compressor blades. The residual may have gone through the engine and caused damage on the turbine wheel. The latter doesn't really make sense though since an entire turbine blade is missing. You would typically see damage on all blades in this case.

What were you doing when this happened?

 

[Danandersen]

Hi Guys, so here are some more pictures that should explain your questions.
Durablack2 - unfortunately I was not around when this happened, but another Tech of mine told me there was a small fire around the turbo ( I would assume from the oil spraying everywhere) and then, yes, oil everywhere. and the engine was not maintaining frequency.

Notice how the brass bushing seems crushed and out of round.

 

[SwinnyGG]

That is a massive, catastrophic failure.

You sucked something through the engine and jammed the turbine, or something.

What does the inside of the turbine housing look like?

 

[Danandersen]

jgKRI,

Yeah. Im pretty sure that the blade off of the compressor wheel is what caused this. I did a compression test on all cylinders and everything is within specs.

here are the pics you asked for

 

[SwinnyGG]

Where was the broken-off turbine blade which you recovered?

The wear on the compressor wheel and cold side housing, along with the failure of the center section, indicate that the center section experienced a VERY large thrust load, which it is not designed to accommodate.

The wear on the cold side parts is there, but not catastrophic- i.e. it appears that no loose debris was produced. There is scuffing but no deep grooves that would indicate a piece of debris trapped between the compressor and cold side housing. Because of that, it appears to me to be likely that whatever went through this engine and grenaded the turbine came from somewhere after the compressor- which means inside the engine somewhere.

Compression tests will tell you very little- you could have bent rods, cracked pistons, bent or stuck valves, broken rockers, bent pushrods, etc etc etc and still pass a compression test.

You need to do a complete teardown and inspection of the entire engine, not just the turbo.

 

[Danandersen]

Hi jgKRI,

I located the Blade in the exhaust line, about 1 foot downstream from the Turbo.

I see your point on having something break off from the inside of the engine - it sounds a bit scary to me, I ran a borescope into all of the cylinders, and did not see anything, there was also
no damage of any kind to any of the spark plugs. (natural gas engine)

To give you a little insight in the operation of the engine it is run for peak shaving and it runs for 9 hours a day. so it is started and stopped
every day. I have now found that the Pre-post lube pump has not been running for roughly 4 years. leaving no lubrication prior to the engine starting, and no post lube either - would you be
willing to consider the fact of lack of lubrication would cause some of the damage to the turbo, maybe in terms of thermal stress? I see the turbo shaft is discolored. But I would not necessarily know how it would explain the broken blade.

I really appreciate your input, thank you

 

[gruntguru]

I have no problem accepting this as a failure that originated in the bearing itself. Inadequate pre and post lube leading to premature bearing wear, eccentric wear in the floating journal bearing, shaft (and bearing) whirl, wheel-housing contact and catastrophic failure.

je suis charlie

 

[TugboatEng]

Where is the thrust bearing?

I had an ABB RR151 come apart in a similar fashion. Chipped blades on the compressor wheel and bent blades on the turbine wheel. There was surprisingly little damage to the compressor and turbine housings considering the rotor hit the compressor housing so hard it pulled pulled 10mm Timesert style inserts out of the aluminum compressor housing. It also caused the cartridge to rotate and sheared the oil lines off of it. The second turbo suffered a simila but not as catastrophic demise. The turbos were newly overhauled and grenaded after about 30 minutes of run-time and while throttling down.

As far as I know, the thrust bearing was absent from the turbo after the failure.

 

[SwinnyGG]

I have personally never seen a turbo failure this catastrophic from bearing wear/failure alone, but I have no problem with the fact that just because I haven't seen it doesn't mean it's not true. My experience with turbos is in the high-performance engine building world, where if failures happen, it's on the dyno when things are brand new.

So perhaps my posts have been leading you down the wrong path. Sorry about that.

If the unit has been running that long without lubrication, all sorts of bad things are bound to happen.

 

[catserveng]

A couple of references you may find helpful, first

http://dieselclass.com/Engine Files/Turbocharger Failure Analysis 3-09.pdf

This a good general overview of turbo failures. Also if you can find a copy of the Caterpillar publication SEBV0550 "Turbochargers Applied Failure Analysis" you'll find some failuer modes pretty close to what you see on your unit.

I think you already have your answer, cold starts and hot shut downs on a generator set starting and stopping everyday without a prelube/postlube cycle. Unfortunately have seen a lot of this type failure in heavy duty engines, why in many cases prelube pumps are added.

From your pictures it seems like you suffered a hot end bearing failure, when a turbo shuts down hot, with the shaft still spinning and no oil flowing the oil cokes around the hot side seal and bearing, forming abrasive particles. At restart, especially on a genset, engine zips right up to rated speed, shaft is spinning and can be running "dry" for several seconds until the oil galleries fill up and gets oil all the way up to the turbo bearing housing. Gives all those nice hard little particles of carbon you generated from the hot shutdown a chance to grind away at the bearing and seal areas. As this process repeats the bearing clearance at the hot end increases, starts to cause contact between the turbine wheel and turbine housing, putting further strain on the hot end bearing and seal area, accelerating the wear. When the wear on the hot end becomes bad enough, the cold end bearing starts to stress and begins to wear on the outer edges since the shaft isn't being held straight anymore. As the wear progresses, the compressor wheel can also start to make contact with the compressor housing, as these contacts start to occur, now the turbo shaft gets slammed back and forth, impacting the thrust bearing. As the hot and cold wheels continue to make contact, they get out of balance, putting even more stress on the already worn and damaged bearings and seals. Unless you pickup a performance problem, the likely end result is a failure like yours. The final phases of the failure accelerates rapidly.

There may be other contributing factors, and without actually doing a root cause failure analysis is hard to tell exactly what happened. But as you provided more info it seems like you pretty much have found your root cause.

Hope that helps, MikeL

 

[turbomotor]

Please humor me while I state the obvious - in a failure like this, the challenge is finding out what failed first and precipitated the subsequent destruction. With a turbocharger spinning fast, the subsequent destruction will be over in a second or two, and you are left with a difficult mystery.

That said. I would not rule out turbine wheel blade fatigue, as the failed blade stub does not show signs of being bent by impact prior to the loss of the blade tip.

My suggestion is to get your favorite metallurgist to carefully clean the turbine wheel and then look for the tell tale signs of fatigue initiation.

While the bearings are distressed, I have looked at many bearings that are in worse shape and still they were only associated with a soft failure, as opposed to the relatively complete destruction shown in your photos.

Do you have any obstruction in the exhaust pipe near the turbine outlet that may create a wake and set up a blade vibration, which may lead to high cycle fatigue of the blade?