Galvanic Corrosion - stainless tank, copper fittings

[Nofossil]

Well, after 9 years of operation, I have a leak in my unpressurized storage tank. The copper DHW coil is leaking into the storage tank. I haven't found the leak yet, but I suspect galvanic corrosion.

In my setup, the water is storage stays there. The copper pipes now have a black film on the surface, and white crumbly deposits at the solder joints and where the copper fittings connect to the stainless pass-through fittings.

In this configuration, any best practices to extend the time before this happens again?

I promise pictures as soon as I drain it.

 

[Karl_northwind]

I assume it's steel? I would think some fancy di-electric union fabrication stuff. 1" di-electric union coupled to 3/4" or whatever the coil is. pass the pipes thru the brass union half (grind out the stop) and solder additional stuff on once it's in place. pics will help.

 

[tom in maine]

This is an interesting issue that seems to crop up with copper. We see it happening at times from the inside out, depending on groundwater.
All our DHW coils are now stainless steel. They work the same and are less expensive. No joints in tank.

As you probably know, the black coating is tarnish, which is what keeps copper from corroding. The pass through might keep the tarnish layer from forming, which would be at the root of your leak.

 

[jebatty]

Have you done a water test on your storage water? pH?, sulfites? etc? Do you use an oxygen scavenger in your water water storage?

I see white crumbly stuff on my Termovar unions, copper/brass; I pulled them apart, cleaned easily, made new gaskets and reinstalled. will now see if they leak when the system is fully pressurized when the heating system if first fired up this Fall.