Gas Turbine Shaft Scoring

Do you have a picture of the damage to the journals?

yes i have , but i cant find any option to attach photo here. can i email it to you ?

You should have a little camera icon on the tolbar above where you type your message. Click on it and attach as a jpeg. If you are usiing Google, this will not appear though.

I doubt anyone here will be able to tell you exactly what happened. Something got in there. I suspect that if you were to look at bearing surfaces under a microscope, you might see similar patterns. Really the only thing you can do at this point is to thoroughly clean everything prior to reassembly. I'd install new bearings also and make sure to prelubricate everything. Before restarting it probably wouldn't hurt to filter all lube oil to insure it doesn't have any contaminants in it. High seal oil drain temperatures could also indicate undue friction at bearing surface. It's also possible, that due to the shaft being a harder material than the bearings, that whatever abrasive got in there, ground the bearings smooth and only left markings on the shaft itself.

Did you check up the babbit thoroughly? I have seen foreign material embedding in the soft matrix and working like sand paper to score the harder material.

Yes i have and thats why i am very amazed. There is nothing on the babbitt. I will send the babbitt pictures also.

The type of scoring however exactly looks like that. It almost seems like some sand or similar small particle had been dislodged from pipe line and embedded into the babbit.

Is it the FWD journal (Inlet side) or the AFT (Exhaust) side?

Model/make? The one I am familiar with has the FWD side fed through cast pipe through inlet casing and I have experienced scales and other contaminants on the pipe surface. In fact even the cast iron powder itself might dislodge through the drilled feed hole. Of course Aft is slightly better off.

The scoring does look like created by very small particles and may be the only reason it was not intercepted by the LO filter may be due to its origin being post filter.

This is GE 7 FA Turbine and exhaust side bearing. Lube oil filter was found dirty, we have taken oil samples and tests are being done, awaiting for results. Some foreign particles are found in the oil, i am waiting for the test results if they are antimonium then it will lead to babbitt dislodging and if they are silicon then may be flushing was not done properly before commissioning.

Did you checked the four ball test & contamination of lubricant?

how much dynamic & static load between shaft & journal bearing?

did journal bearing have oil groove?

Are you sure the shaft was in pristine shape before the thing was assembled?

Updates: We had throughly checked bearings and found the lower half to be damaged. Hard materials were embedded on to the surface and it was behaving like a sand paper. The shaft has been lapped and scoring marks removed. The babbitt was sent to workshop for repairing but NDT tests revealed that the hard materials are penetrated much deeper inside and we have to re babbitt the bearing (since spare is not available right now). My previous experience with re babbitting of bearing is not very good. There was some pores left inside and the material came off during the operation. Any suggestions / recommendations regarding how to ensure that re babbitting has been done successfully ? We are also planning to flush lube oil in the mean time to remove all the foreign contaminants... Any more measures shall we take?

Good feedback. Not often that we get that.

Spin cast repair by reputable engineered bearing manufacturer. Casting and or puddling can work but is a bit dodgey if not done right. Are your bearings "round". If profiled, then machining becomes a special task for a good specialist with the right equipment.

Not sure where in the World you are - these guys are in South Africa, but with connections/licences all over. Some of the other names on this site may be of interest (usual disclaimer).

I am in Suadi Arabia. Yes this is round. The babbitt will be machined after the material depositions as per the required clearances. I am also concerned about the quality of re babitting but GE is doing thisso i guess i should not worry. I will update, if something special occurs.

GE has the right procedures and quality control to do this in their approved shops. Should not be a problem.

The old Guest .

Did you check up the embedded particle? That will give you quite a good idea of the source.

Check the lube oil line thoroughly.

BTW: it is on FWD side or the AFT side? (never mentioned) ? This will give you further clue about the source.

re-babbitting is acceptable process no doubt, but the problem is re-machining after re-babbitting. The center-line is offset as well as the inside diameter is kept slightly lobed in a few of the models.

We used to face a lot of problems in re-babbitting too though it is perfectly feasible and a bit extra care is necessary.

Did you try to buy the bearing itself from GE/ other reputable suppliers? I don't think it will be too costly.

Sorry missed your post. AFT side bearing -

So the whole line is steel and pipe lines, no Nodular CI in the way. Also filter choked.

Any sort of sealing problem? especially in the base frame or more probably in the deflector sealings of the inlet (less likely outlet) through which sand / dust may enter and accummulate in the lube oil?

Though the choked filter should have given the DP high alarm

Age of the turbine?

While you may not see any damage to the bearings I would have them checked to see if the bearing match the scoring.

electrons move in metal to fill in gaps so if the bearings were not perfectly smooth when installed this could be just electron drift in the metal.