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This has appeared under a kitchen sink... hot water inline feed only. It appears to have started after I put a quarter turn ball shutoff valve in a couple years ago. You'll notice the new shutoff valve is also looking strange, corroded or encrusted with something. Its mostly red (not as bright red as the photos, they really bring it out) and also white crust. While the pipe joint is moist, its not dripping at all, and there is no problem with water flow or any discoloration of the hot water.

Galvanic corrosion? But why here, there are galvanized pipes all over this older building with stop valves put on, this is the only one rusting like this. The location and age of pipes would make this a nightmare to replace, and I fear the pipe threads are rusted together so no removing.

Is there a danger of bursting? It doesn't seem so but that is my worst fear. Its not even dripping. What if I wrapped the whole thing in Flex Tape?
I've made Flex Tape repairs on hot water lines that have lasted decades. What if I sprayed Rust Neutralizer on it first, would the tape still stick? Epoxy? Naval jelly to remove rust & repaint?

It seems there would be some cost effective smart solution along the lines of 'if it aint broke don't fix it'. Anyone can tell you to rip out and replace. Yes if I were made of money. I am sadly not.

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  • Clean the main inlet, replace all components above with PVC. That valve has been drip leaking for long time, You have clack build up. Clean with vinegar.
    – Ruskes
    Jul 14, 2022 at 6:07
  • This would involve tearing out the wall and a massively expensive job. I CAN'T AFFORD THAT. And by that I mean, I have $100 left in the bank to last me the rest of the month. The parts are rusted on obviously and can't be removed. Again I've wrapped components with pipe tape and they've lasted decades. I'll keep looking I know there's a smarter answer than this.
    – C Rutherford
    Jul 14, 2022 at 11:13
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    Not necessarily. How much "wall" does the pipe go through? You may be able to get a new length of pipe to slide into the same hole in the wall or bore a new hole next to the existing pipe to run new pipe through. PVC pipe, valves, elbows, and corollary materials should be pretty cheap ($25?) compared to the cost for repairs/replacements when the pipe lets loose. Replacing the pipe is the smart answer here. There is no repair for this.
    – gnicko
    Jul 14, 2022 at 14:57
  • In the last picture is the sink trap dripping/leaking? If so that doesn't help matters.
    – Platinum Goose
    Jul 14, 2022 at 15:05
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    You could wrap the pipe till the wall, but what happens when the pipe starts leaking inside the wall. The wall pipe looks like it has some removed metal already.
    – crip659
    Jul 14, 2022 at 17:41

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Galvanic corrosion hits the connected metal element with the lowest potential. This is why ships with a steel hull have a zinc anode installed - that will be the cheap sacrificial part that rusts away rather than the hull itself.

In your case I'm not sure what other metal elements are touching (directly or indirectly, it's electrons travelling we're talking about here - and I assume the pipe that goes into the wall is also metal), but it appears that elbow joint of yours has the lowest potential, and therefore becomes the sacrificial element.

It will spring a leak eventually (coincidentally we just had a leak fixed because two decades ago the contractor decided to use uncoated steel pipes embedded in the concrete flooring), but probably not right now (as in, the next days and weeks).

The thickness of that rust layer does suggest you should not be postponing it too much though, so right now I would suggest having a look at what that rusty section is (electrically) connected to, and which metals are used. This chart shows you which combinations are risky. Then you know what should possibly be replaced next to the rusty element itself.

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There is already a leak somewhere (you mentioned that the assembly is moist). It needs to be disassembled, have any badly corroded pieces replaced, and then reassembled with good quality joint compound or joint tape, making sure that everything it tight (but not over-tightened).

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Can you slap a FlexTape band-aid on it? Sure, why not, it's your place! (You're not renting, are you? If you are, call the landlord immediately!)

Will this band-aid last "decades"? It might, but you probably don't want to count on it. You'll probably have a really hard time wrapping the bit of pipe running through the wall, too.

The real issue is that when you replaced the valve a couple of years ago, you didn't get the joint sealed properly and it's had a very slow leak for a couple of years and now your metal pipes are rusting. The only real solution is to replace all the rusted metal.

This appears to be a very short bit of plumbing, so it shouldn't take a lot of replacement pipe to fix it. A couple of fittings to mate up with the valves (replace the valves too, if they're corroding, may as well do it right), a couple of elbows, and the shortest stick of pipe you can buy at your local store. (Eyeballing from this side of the internet, I'd venture to say you could get away with 24" of pipe and still have some left over. YMMV.) Honestly, the full cost of supplies to do this right probably won't be significantly more than the cost of a roll of "repairs anything" tape anyway.

Will this burst tomorrow? Maybe. But, it's taken 2 years to get to this point, there's a possibility it'll take 2 years or more until it fully lets go. But, it could go tomorrow, you never know. The point here is that you probably don't have to replace it this weekend, but that "sooner" is definitely better than "later".

If money is really tight, you can probably find a small luxury/vice you can sacrifice this week to buy a couple of parts, then another small luxury/vice you can sacrifice next week to buy a couple more parts, etc. (Buy the parts immediately, don't save up to buy them all at once - cash on hand can be too tempting to spend on something more fun.) Once you have everything you need, take a Saturday (or other non-work day) and dig in bright and early to give you the most time to get it all done (and run to the store for that one last "Darn, I didn't think about that!" item you'll likely need).

Oh, and make absolutely sure you get all your joints sealed properly this time so that you don't have that little bit of moisture seeping out again. If you don't get it sealed tight, metal plumbing will be right back in this condition in another couple of years. Plastic plumbing will last, but you'll have moisture collecting in your wall ruining it, and under your cabinet, ruining that. Repairing/replacing those in another couple of years will make the budget for this look puny.

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They are corroding because they are wet, leaks or condensation. The zinc corrodes first ( more or less white) then the iron corrodes , red/brown.

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the chromed brass valve connecting to the iron pipe is the main cause of the corrosion, replace it with with a PVC one.

When you can afford it replace a much of that rusty pipe work as possible with with new galvanised ones or plastic ones.

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