Thread: dielectric connections/corrosion

I have seen copper/galvanized corrosion. I am curious about brass/galvanize unions,
or for that matter copper/brass unions. The ones I have seen , mixes as such, in
the same plumbing systems appear to have very little corrosion.Any details out there?

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Stephen,
There are many opinions about this subject. I use galvanized steel couplings with phenolic plastic inserts that provide a way of joining dissimilar metal pipes while stopping current flow through the pipes, which is a cause of the galvanic action that corrodes the pipes. I have also seen recommendations for installing sacrificial anodes in the lines, (similar to those in water heaters) to stop corrosion.

In theory, the water itself, (with the right mineral or metal content), could conduct electric current and circumvent the insulating coupling.

It would seem that in some locations, the water itself is corrosive to various metals and nothing can be done to stop the corrosion. That was the case in Phoenix where I used to live. The water would tear apart galvanized pipe with no other metals present. I also had a customer with an all copper house have pin-hole leaks start when the house was only 10 years old.

Food for thought,
Tim Lorenson

I was thinking along the line of using brass unions to join different metals.

I have joined copper to brass to galvanized with no local corrosion at the joint but there is still current flow and corrosion may happen in other areas.

Galvanized unions have a brass or bronze seat in one half of the union to provide a better seal.

Bronze is an alloy of up to 88% copper and 12% tin
Brass is made from copper and zinc
Galvanized pipe is coated in zinc
That would explain why brass plays nice with copper and galvanized pipe.

Tim Lorenson

Thanks Tim
If water can be an electric issue , Would a bonding jumper across the union,be
a reasonable fix , and would it possibly be a long term cure?

Originally Posted by Stephen DeCosta

Thanks Tim
If water can be an electric issue , Would a bonding jumper across the union,be
a reasonable fix , and would it possibly be a long term cure?

Stephen,

Oooh! Interesting thought. It seems to me that since it is required to bond the plumbing system and the dielectric unions isolate the pipes, it would be necessary to bond across the union.

Stephen said: "It would seem that in some locations, the water itself is corrosive to various metals and nothing can be done to stop the corrosion. That was the case in Phoenix where I used to live. The water would tear apart galvanized pipe with no other metals present. I also had a customer with an all copper house have pin-hole leaks start when the house was only 10 years old."

In my area we had batches of galvanized material used in tracts from about the mid-seventies to early eighties that were inferior galvanizing. I believe that the material came from China. Whole tracts built during that time have already had all horizontal runs replaced already and many have had the verticals replaced (at least the smart home owners have done so). The symptoms were many pin holes (often sealing themselves again) and heavy interior corrosion on the bottom sections of piping, with evidence of exterior corrosion as well.

I am not sure just how broad the distribution of this inferior material was but I'll bet Phoenix got some of it. We have homes built in the 20's through the 60's with galvy piping that are still going strong (of course with some restriction at pipe interior) showing no signs of leakage what-so-ever (except at the occassional fitting where thread area is the culprit.

Be on the lookout for galvy piping from the mid-seventies to the early eighties.

Mitch T.