HDZ Fasteners Corrosion 1

[saymeng]

Hi, I need some advice/suggestions on the root cause of this. The HDZ bolts are used on the LV side of a transformer and it shows signs of corrosion. The location is in doors, dry, no signs of moisture ingress. The transformer has been in operation for 3 years+.

 

[EdStainless]

What is corroding?
A closer picture would help.
What kind of facility is this inside of?

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P.E. Metallurgy, Plymouth Tube

 

[saymeng]

Hi, here is a close up. It looks to me like the zinc is migrating...on the bolts.

http://files.engineering.com/getfile.aspx?folder=eb4bdc7c-f284-467b-8f5f-a46d29a9e8e0&file=TFM2.png

 

[EdStainless]

What is the environment?
The Zn is supposed to be the sacrificial coating. It corrodes to protect the steel.
I am guessing that you see Zn oxide.
This has been wet, maybe condensation?

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P.E. Metallurgy, Plymouth Tube

 

[CoryPad]

What is the plate material under the fasteners? It looks like it may be corroding. Your second photograph does not have enough resolution to determine what is corroding. You need to challenge the assumptions of dry/no moisture ingress.

 

[saymeng]

Hi All,

It is unlikely to have moisture ingress, it is a energised distribution transformer that has been in operation for about 3 years. It is location in-doors.

I am sorry but that's the best picture I can get, as the client is reluctant for us to open up the LV cable box.

Yes, I agree that Zn is sacrificial coating, but what is strange about this situation is that the connection is running "hot" most of the time (approx. 140F). The copper bars are tin coated.

I an just throwing this question out here, by any chance could it be due to some form of organic gas? At the present time I have not visited the site.

Thank you

 

[EdStainless]

Yes, you say indoors, but the air in most factories is much more corrosive than sitting outdoor ever could be. What is this being exposed to?
What is the base material and surface coating on the mating part?

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P.E. Metallurgy, Plymouth Tube

 

[saymeng]

Hi,

The fasteners are all hot dipped galvanized steel and the copper bar is tin coated.

Thanks