Home>Discussions>PLUMBING>Replace Galvanized Iron Pipes
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househelper
Re: Replace Galvanized Iron Pipes

You are right. Iron is a stronger reducing agent than copper. Brass is just an alloy of copper with zinc.
Connecting brass to iron even though the brass is an alloy will still lead to corrosion.

The iron in presence with copper through water creates an electrolytic cell where the iron corrodes and plates on the copper. Only by spacing the copper from the iron through rubber can the electrolytic cell fail to form and prevent this galvanic corrosion.
Evidence of this is present in my kitchen drain pipe where a brass trap was connected to a galvanized iron elbow.

The iron pipe got clogged and broke off.

This new project will require that I replace drain pipe with plastic PVC pipe. I will have to move kitchen counter to get access to wall pipe.
What special connection is required to connect PVC to existing iron pipe?

Fencepost
Re: Replace Galvanized Iron Pipes

Househelper,

I'd recommend a rubber coupling ("Fernco" is a well-known name) for joining PVC to iron drain pipes. Or, if the drain pipe provides a good threaded connector, you can use a threaded PVC connector.

As a rule of thumb, PVC, ABS, and iron all have the same outside diameter, known in the trade as IPS (Iron Pipe Size). There are exceptions: I think storm drain pipe used in exterior underground applications may be a different size.

Gray Watson
Re: Replace Galvanized Iron Pipes

Galvanized steel

Iron

Black pipe (gas)

Not the same thing.

Drain Waste Vent plumbing

Gas plumbing

Potable plumbing

Not the same thing.

Don't think shark-bites allowed in closed walls.

6-8" bronze or brass between Galvanized to Copper. A short dielectric union with a rubber or plastic isolating gasket which won't last but a few years won't do.

Fencepost
Re: Replace Galvanized Iron Pipes
Gray Watson wrote:

Galvanized steel

Iron

Black pipe (gas)

Not the same thing.

Drain Waste Vent plumbing

Gas plumbing

Potable plumbing

Not the same thing.

But still the same outside diameter. There are two trade sizes: IPS (Iron Pipe Size) and CTS (Copper Tube Size). All of the above are IPS; CPVC, Polybutylene, PEX, and copper are all CTS. Polyethylene (black plastic) may be CTS, or it may be its own thing (constant ID, variable OD depending on wall thickness). And garden hoses are "who knows?"

Quote:

Don't think shark-bites allowed in closed walls.

Could be. I have zero experience with these, except for seeing them in the store and thinking "hmm, what will they think of next?" and "too expensive, I'll just use the traditional parts."

Quote:

6-8" bronze or brass between Galvanized to Copper. A short dielectric union with a rubber or plastic isolating gasket which won't last but a few years won't do.

Nope, wrong answer. If you can get an electrical continuity test between the galvanized and the copper, you need a dielectric union. Or a length of plastic pipe. Just putting bronze or brass in between is insufficient.

Gray Watson
Re: Replace Galvanized Iron Pipes

Read again what I said about a short dielectric union.

Comments from someone who doesn't know what Galvanic Corrosion is and is not and one who recommends using pex to a flushometer.:p

Another thing that cannot be enclosed in a wall.

....Sigh! :rolleyes:

Fencepost
Re: Replace Galvanized Iron Pipes
Gray Watson wrote:

Read again what I said about a short dielectric union.

Comments from someone who doesn't know what Galvanic Corrosion is and is not and one who recommends using pex to a flushometer.:p

Another thing that cannot be enclosed in a wall.

....Sigh! :rolleyes:

Comments from someone who can't post coherently. :confused: If you have a metal-to-metal (i.e., galvanized steel to brass to copper) connection, you will have "Galvanic Corrosion," also known "electrolysis." (EDIT: Oops, my bad. See next post.)

It's true that you can use brass fittings with galvanized/steel/iron pipes. It's also true that you can use brass fittings with copper. However, you should never mix copper and steel in the same plumbing system unless they are "electrically" isolated. If you have a piece of plastic pipe between steel and copper, and you run a jumper wire from the steel to the copper, you will experience electrolysis.

That brings up an interesting problem: building codes generally require that metal water pipes be connected to the building's electrical ground. This is necessary from a safety standpoint. However, if you have a mix of copper and steel pipe in the same water system, how do you comply with the electrical code when to do so could induce corrosion of the pipes? It may be that if the grounding is done properly -- say, a star configuration -- that there won't be a problem. But I can't answer that because I'm not an electrical engineer.

Anyway, we're getting into an esoteric discussion that's probably not helpful to the original poster.

Fencepost
Re: Replace Galvanized Iron Pipes

I have to apologize for using incorrect terminology. I have used the term "electrolysis" where I should have used "galvanic action" (or "galvanic corrosion," as another poster has used). A little bit of online research has revealed the following:

Galvanic action and electrolytic action (electrolysis) are essentially opposites.

In galvanic action, dissimilar metals (electrodes: anode and cathode) in an acidic or alkaline solution (electrolyte) will have a voltage differential (potential) between them. When they are electrically connected, as with a wire or if they are touching, electrons will flow from one to the other, and a corresponding chemical reaction will cause metal to flow through the electrolyte from one electrode to the other.

Electrolysis is a process where you apply, from an external source, an electrical current between two electrodes in an electrolyte. Where the electrodes are dissimilar metals, this also causes metal to flow in solution from one electrode to the other. (It is also the process used to crack water molecules in the production of hydrogen.) Applied correctly, electrolysis can reverse the galvanic process.

To generalize, when a battery is being discharged (i.e., in a flashlight), the process is galvanic action. When the battery is being recharged, an electrolytic process is used.

Again, I apologize for misleading anyone who has read my previous posts.

househelper
Re: Replace Galvanized Iron Pipes

How can you connect galvanic iron pipe to pvc? Are there any screw on fittings? Or do you have to use some sort of band that you use a screwdriver to tighten?

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