Hardfacing in a 230kV Transformer?

[SMF1964]

Anybody have any idea what a Co-Cr-Mo alloy would be doing inside a 230/69 kV transformer? The compartment in question has a copper blush of copper and copper-zinc particles over much of the surfaces, but mixed in with this debris are particles of this Co-Cr-Mo material (58Co-31Cr-11Mo). Any thoughts?

 

[NickE]

No Moly or Nickel? other wise that is kindof close to elgiloy....

(not that I know why it would be in a transformer... Ecept it is really really strong and non-magnetic)

 

[SMF1964]

11% molybdenum but no Nickel.

 

[NickE]

ooopss... that was supposed to be:

"No Iron or Nickel?"

Good luck anyway...

This might help:

http://www.matweb.com/search/GetComposition.asp

 

[EdStainless]

Any carbon?

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Corrosion, every where, all the time.
Manage it or it will manage you.

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[SMF1964]

Less than 1% iron (SEM/EDS measured 0.8%). As for carbon, the EDS cannot measure carbon, so I have no information on the carbon content (if any).

That being said, the particles are 5-25 microns across and appear to be flakes/chips, so even if I were able to detect the carbon x-rays, there would be the question of whether the carbon signal is from the particle(s) or from the polymer based filter used to catch them.

I can make some estimates about the material - qualitatively the BSE image is similar to the adjacent copper particles, so the average atomic number is about the same as copper. Thus, I can rule out this material as being all oxide or a significant amount of carbon, else the brightness would be different, 'kay?

 

[metengr]

SMF1964;
I talked with our electrical experts who happens to sit in an office down the hall from where I reside. He mentioned to me that other than iron laminations (iron/silicon steel), copper turns and nonmetallic bushings/insulation, the metals you had reported should not be present. There is no hardfacing in transformer compartments.

I know that sometimes in the field that transformer oils are changed out. Could it be that you had a batch of contaminated oil?

 

[SMF1964]

metengr:
Thanks for the info. To quote Mr. Spock: "There are always possibilities." (actually, that would be quoting William Shatner, playing Capt. Kirk speaking at Mr. Spock's funeral as he quoted Mr. Spock. But I digress.)

We've had a number of issues with a sister transformer at this facility - that one failed (albeit not spectacularly) and disassembly found a rather thick layer of copper dust coating the inside of the compartment - 100ml of that oil filtered through a 0.8µm filter turned the filter brown/copper colored. The concern was that this other unit would be in danger of problems, since they were of similar vintage. We have a rather solid oil testing program here, but I don't recall testing for metals. Of course, I would expect that they would fail on dielectric or power factor before the metals get too out of hand, but then I'm just a humble metallurgist.

 

[kclim]

Are the compositional values you quoted 58/31/11 obtain from the EDS measurements? I wouldn't take those figures as gospel if that was the case; EDS is semiquantitative at best.

I'm not sure about particles of Co-Cr-Mo, but isn't Cobalt used as an alloying element in magnets? The chromium and molybedenum might be coming from stainless steel (?).

Chromium may also be present in rust inhibitors and molybenum in lubrication.

Also, it should be possible to pick up some semblance of carbon under EDS, although the atomic number is light. Normally shows up as a peak in the very low eV range.

 

[SMF1964]

kclim: I agree that SEM/EDS is not a certifiable, fully quantitative method for chemical analysis, but it is certainly comfortable to say that a 58/31/11 Co-Cr-Mo measurement is within 2-5 percentage points of the 'correct' composition (i.ei, 55-60Co, 28-35 Cr, 8-15 Mo).
Yes, cobalt is used in some hard magnets - I hadn't thought of that. As for rust inhibitors (we use DBPC, an organic hydrocarbon type material, in our transformer oils) or lubricants for Cr and Mo, I don't think that's the source for this, since the transformer oil is kept rather clean in terms of additives (beyond the DBPC inhibitor).

You are correct in that the electron microscope can pick up carbon qualitatively, but past experience with my instrument shows a very insensitive detection capability. I've tried to analyze graphite nodules in a low alloy steel (another story) and detected only a moderate size peak among significant iron signals in what should have been almost 100% carbon. Given that I was looking at very small particles of this Cr-Co-Mo material, as I stated earlier, I had no confidence that the minimal carbon peak I was getting was not from the filter media used to capture the particles and upon which the particle was resting.

Steve, out

 

[metengr]

The core of a main power transformer usually consists of iron-silicon textured sheet (lamination) steel with copper windings to provide for the step down in voltage. I have not come across the use of iron-cobalt alloys in our main power transformers.

Keep in mind that depending on the size of the transformer, the oil (non-PCB I hope) used in the transformer compartment can be circulated thru external radiators and pumps to provide for cooling. Pump seals or bushings could provide a source of metal contamination.

From one utility metallurgist to another.

 

[EdStainless]

There are a lot of Co-Cr-W wear resistant alloys. These would be common in shaft seals for a pump. The only Ni free Co-Cr-Mo alloys that I know of are bio-med implant alloys.

Other than wear material from a pump, the only other thought that I have is how do they alloy for thermal expansion in the transformer? Is part of the internal structure resting on skid pads to support it, but allow some motion? Could those be hardfaced?

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm