Steam turbine bearing housing repair

[migueldiazch]

Hello,

I am looking for some advise about how to repair some craks on a cast iron NDE bearing housing next to ball bearing working area.

See attached file.

Regards.
M.D

 

[vpl]

Miguel

What you posted was a cross-section view of a turbine, complete with customer information. While it shows the general location of the bearing housing, it doesn't give any information about the types of cracks you're experiencing.



Patricia Lougheed

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[migueldiazch]

Patricia,

The document has 3 pages, see pages 2 and 3. Thank you very much for your help and interest

Regards,
M.D

 

[vpl]

My bad; I was obviously in too much of a hurry when I glanced at the drawing!


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[GPRnD]

There are techniques that can stitch cast iron together using special fasteners. However given your location (on a shoulder) I don't think they would work.

You could try to weld repair by gouging out the crack, welding with a nickel based rod and then remachining. My concern would be that this is a high stress area which contains the thrust bearing (and probably the reason why it cracked in the first place).

Weld repairs of cast iron are not viewed (at least in my experience) as being structural. Thus I'd be concerned about future failure.

If it were up to me I'd simply buy a new bearing housing. You will spend a lot of money trying to repair it and still have a repair of unknown longevity.

 

[Compositepro]

It looks like the cracks are only near the part-line for that casting and may have been caused by improper assembly of the parts. That is, the damage occurred during assembly. If that is the case, you may not need to repair the cracks, just be more careful during assembly. The now wider slots will now allow for easier alignment when trying to assemble the split casing, but when fully assembled the bottoms of the slots, where there is no cracking, will keep all the parts in proper alignment.

 

[bingopin]

I would consider grinding out,welding with minimum heat input, and machining back to proper dimensions. Thrust loads should be relatively small...that's why it has a simple radial ball bearing as a thrust bearing.

 

[JJPellin]

I have seen many failed bearings and bearing housings in turbines with this basic bearing arrangement. But, I have never seen one fail at that location. This turbine should produce very little thrust. Something very bad happened to this little turbine. There should not be much load on that shoulder. I would not consider it acceptable to weld a cast iron housing of this sort. You would have a high chance of distorting the housing and causing other problems. Metal stitching could be done. But, it would cost more than a new housing and we would still not consider it a permanent repair. So, as noted above, the best option is to purchase a new housing.

If you have urgent need and cannot afford the downtime to wait for the new housing, you have a few options. As already noted, you can metal stitch. I would prefer a fabricated solution. I would have our machinist cut out the affected area. He would make a bolt-in insert which could be machined in place back to the original dimensions. This would restore the critical fit of the thrust bearing within the housing and would probably be stronger than the original cast iron pocket. Depending on the final design, I might consider this a permanent repair. But, I would most likely order a new housing anyway.


Johnny Pellin